docs: correct the bot-score claims behind the browser poller

Every doc statement that explained a Cloudflare challenge as a "score"
was wrong. Researched against Cloudflare's own docs on 2026-08-12
(docs/research/cloudflare-bot-scoring-and-poll-cadence.md, 22 primary
pages plus RFC 9309): the 1-99 bot score is Enterprise Bot Management
only, free-plan zones get Bot Fight Mode signature matching and no score
at all, and no per-IP request rate is documented as an input to
challenge issuance. cf_clearance also expires in 30 minutes, so every
cadence at or above 1h re-solves the challenge regardless.

Docs only - no behaviour change. The 6h browser cooldown stays; its
justification is now cost (a serialized single-tab solve costs seconds,
a plain read costs one request), not a risk reduction nothing documents.

- AGENTS.md: the block is per-zone configuration plus request
  fingerprint, not IP reputation; comix.to turning its gate on
  2026-08-12 is the example. Residential egress avoids the
  cloud-hosting-IP signature rather than earning a better score. The UTC
  measurement stands but its mechanism is marked undocumented.
- backend/AGENTS.md: states why the browser cooldown is longer.
- ADR-0003, ADR-0006: dated corrections rather than rewrites. Both
  decisions stand on their other arguments (sweep depth, VPS memory).
- DEPLOY.md: a red smoke run means the Site's settings or this Chrome's
  fingerprint moved, not that "Cloudflare's scoring" did.

AGENTS.md

@@ -18,11 +18,11 @@ Userscript targets **Violentmonkey**, so `GM_*` APIs available, but stay GM-free
 - Cross-origin `fetch()` work **only** against CORS-enabled backend. Manga sites `https://`, so backend **must be HTTPS** (else mixed-content block).
 - Every site is its **own origin with its own `localStorage`** — a shared remote store is the only way to unify bookmarks. Cloud sync required, not optional.
 - Userscript run in **isolated world**, so embedded API token safe from site's JS.
-- Cloudflare's block on manga sites **IP-reputation-based, not universal — and not reliably reproducible.** Verified 2026-07-26: plain `curl` from both CGNAT dev machine *and* deployed VPS got clean 200s with real HTML on both asurascans.com and demonicscans.org (homepage, series, chapter pages) — no interactive Turnstile challenge from either IP at test time. Contradicts earlier untested assumption CGNAT dev IP blocked; wasn't, at least this date. Treat "does curl work right now" as live, time-varying fact to re-check, not fixed property of machine — Cloudflare's bot scoring can flip previously-clean IP without notice. Backend fetcher still needs graceful-degrade path for when challenged, and adapters should be **verified against live pages** (Playwright MCP, on-device devtools, direct probe) before finalizing, not assumed from single earlier test.
+- Cloudflare's block on manga sites is **per-zone configuration plus request fingerprint, not IP reputation — and not reliably reproducible.** Verified 2026-07-26: plain `curl` from both CGNAT dev machine *and* deployed VPS got clean 200s with real HTML on both asurascans.com and demonicscans.org (homepage, series, chapter pages) — no interactive Turnstile challenge from either IP at test time. Contradicts earlier untested assumption CGNAT dev IP blocked; wasn't, at least this date. Treat "does curl work right now" as live, time-varying fact to re-check, not fixed property of machine — a Site can turn its protection on overnight, which is exactly what comix.to did on 2026-08-12. An earlier version of this line blamed "Cloudflare's bot scoring"; that was wrong. The 1-99 bot score is Enterprise Bot Management only and does not exist for a free-plan zone, and no per-IP request rate is documented as an input to challenge issuance — `docs/research/cloudflare-bot-scoring-and-poll-cadence.md`. Backend fetcher still needs graceful-degrade path for when challenged, and adapters should be **verified against live pages** (Playwright MCP, on-device devtools, direct probe) before finalizing, not assumed from single earlier test.
 - **kagane.to and novelfull.com are the exception to the above** — both sit behind a Cloudflare JavaScript challenge no TLS fingerprint clears, so the backend polls them over CDP (`BROWSER_WS_URL`). When that's unset, kagane is skipped entirely (a plain fetch would only retrieve a challenge page) while novelfull pages are still attempted over plain TLS — its challenge is a live time-varying fact and its cover bytes never need the browser. The four other sites poll fine over plain TLS.
 - **The CDP browser must look like a real browser, and stock headless images don't.** Measured 2026-08-08 against kagane.to, all from the same IP: `chromedp/headless-shell:stable` never cleared the challenge in 90s (`navigator.webdriver` true, empty plugin list, Chromium-branded client hints — suppressing `webdriver` alone changed nothing); `zenika/alpine-chrome` ships Chrome 124, refused outright; real Chrome with the default `--headless=new` UA never cleared, because the UA says `HeadlessChrome`; real Chrome with a stock UA **and** a non-UTC clock zone cleared in ~4s. Hence `chrome/` — a Debian image with `google-chrome-stable`, a version-derived UA, and `TZ`/`BROWSER_TZ`. Chrome reads the zone *name* through ICU from `/etc/localtime`'s symlink target, ignoring the file's contents, so mounting the host's `/etc/localtime` does **not** work; `/etc/timezone` is mounted instead.
-- **The browser is not in the API stack and must not be put back.** It's its own compose unit (`chrome/docker-compose.yml`) on a second machine, reached over the tailnet — it held 471 MiB on a 1974 MiB swapless VPS, and a residential egress scores better with Cloudflare anyway (ADR-0006). Consequences that constrain code: `BROWSER_WS_URL` must be a tailnet **IP** (a MagicDNS name 500s at `/json/version`, same trap as the old Docker service name); the CDP port binds to the tailnet address only, since CDP authenticates nothing and that host has a real LAN; and the browser is on-demand (ADR-0005), so an unreachable or asleep one must degrade exactly as an unset `BROWSER_WS_URL` — plain-TLS libraries unaffected, kagane/novelfull logged and skipped, stored covers still served. Never add `chromedp.NoModifyURL`: discovery per fetch is what makes a restarted Chrome invisible.
-- **UTC is the tell, not a country mismatch.** A UTC clock is the datacenter default, so Cloudflare scores it as one; any real zone clears. Measured 2026-08-08, identical container, one Indonesian egress IP: UTC never cleared in 60s (twice), while `Asia/Jakarta` **and** `America/New_York` both cleared in 4s. An earlier note here claimed the zone had to match the egress IP's country — that was wrong, inferred from the host clock (`Asia/Bangkok`) rather than the measured egress. `BROWSER_TZ` therefore needs a plausible zone, not a geolocated one.
+- **The browser is not in the API stack and must not be put back.** It's its own compose unit (`chrome/docker-compose.yml`) on a second machine, reached over the tailnet — it held 471 MiB on a 1974 MiB swapless VPS, and a residential egress avoids the cloud-hosting-IP signature Bot Fight Mode documentedly challenges (ADR-0006; not a better "score" — free-plan zones have no score). Consequences that constrain code: `BROWSER_WS_URL` must be a tailnet **IP** (a MagicDNS name 500s at `/json/version`, same trap as the old Docker service name); the CDP port binds to the tailnet address only, since CDP authenticates nothing and that host has a real LAN; and the browser is on-demand (ADR-0005), so an unreachable or asleep one must degrade exactly as an unset `BROWSER_WS_URL` — plain-TLS libraries unaffected, kagane/novelfull logged and skipped, stored covers still served. Never add `chromedp.NoModifyURL`: discovery per fetch is what makes a restarted Chrome invisible.
+- **UTC is the tell, not a country mismatch.** A UTC clock is the datacenter default, and the challenge refuses it; any real zone clears. Measured 2026-08-08, identical container, one Indonesian egress IP: UTC never cleared in 60s (twice), while `Asia/Jakarta` **and** `America/New_York` both cleared in 4s. An earlier note here claimed the zone had to match the egress IP's country — that was wrong, inferred from the host clock (`Asia/Bangkok`) rather than the measured egress. A second earlier claim, that Cloudflare "scores" a UTC clock, was also wrong: the measurement is real but the mechanism is not documented anywhere — Cloudflare publishes no timezone signal, and free-plan zones carry no score at all. `BROWSER_TZ` therefore needs a plausible zone, not a geolocated one.
 - **A challenged page needs the tab kept open.** The interstitial takes seconds to solve and only then writes clearance into the browser's shared cookie jar. Navigate-read-close never clears anything; `BrowserFetcher.run` holds one tab and re-reads until the payload arrives.
 
 ## Architecture