Poll comix.to through the browser sidecar (#98) (#105)

Closes #98.

comix.to began answering plain-TLS fetches with a Cloudflare JavaScript
challenge on 2026-08-12, so every poll got a 403 interstitial. Its cover host
`static.comix.to` is gated the same way. comix therefore joins kagane and
novelfull as a browser-backed Site.

## What changed

- **Registry** (`internal/latest/sites.go`): comix gains a `Browser` entry —
  `comixRead`, `Done: body != "" && !isInterstitial(body)`, `Fallback: false`.
  Skip-when-no-browser falls out of the existing routing; no site-string compare
  was added anywhere.
- **Read shape** (`internal/latest/browser.go`): an in-tab `fetch()` of the
  Series URL, not a DOM render. comix is an SPA — rendering it costs ~65
  requests for the same server-rendered HTML one fetch returns (24.5 KB,
  ~480 ms measured). `comixSeriesPageURL` pins scheme + host + `/title/<slug>`
  and rebuilds the address, so a client-supplied `series_url` cannot aim the
  browser anywhere else.
- **Cover bytes**: `comixImageURLRe` pins `https://static.comix.to/<path>.<ext>`;
  `BrowserFetcher.Image` now gates on `browserOnlyCoverURL` rather than a
  kagane-only regex, so both Sites' image URLs route through the one path.
  Bytes come from direct navigation, not a page-context fetch — comix's Series
  page sets `cross-origin-embedder-policy: require-corp`, which fails one.
- **Parsers and stored Series identity: untouched.** The in-tab body is the same
  server-rendered HTML the existing fixtures were cut from.

## Verification

- `go test ./...` green (needs Docker).
- New seam tests: comix routes to the browser when one is configured, and is
  not fetched at all when none is (`TestComixUsesBrowserFetcher`,
  `TestComixSkippedWhenNoBrowserFetcher`); URL-pin and cover-gate table tests.
- Live proof against the real browser unit, `TestSmokeComix` (env-gated):
  page 24793 bytes in one in-tab fetch, chapter 53, cover accepted by the pin,
  26862 bytes of `image/jpg` retrieved.
- Two-axis review run; findings were stale comments on `BrowserFetcher`, `Get`
  and the `Fallback` field, fixed in f000cc7.

Docs updated: root `AGENTS.md` (constraint + smoke command, including the note
that this dev machine's ISP DNS-hijacks `comix.to`), `backend/AGENTS.md`
(poller, cover pipeline, `BROWSER_WS_URL`), `REDEPLOY.md` §8 degrade note.

Reviewed-on: #105
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

graphify-out/.graphify_labels.json

@@ -18,16 +18,18 @@
   "16": "Cloudflare bot scoring and poll cadence — what is actually documented",
   "17": "Go Code Style Guide",
   "18": "Agent Skills",
+  "19": "Store",
   "20": "I/O Performance Patterns",
   "21": "CPU Optimization",
   "22": "Caching Patterns",
   "23": "Browser Entrypoint",
   "24": "Memory Allocation & GC",
   "25": "Cover Fetcher Tests",
+  "26": "Open",
   "27": "Find Skills Guide",
   "28": "Allocation Patterns",
   "29": "Observability & Alerting",
-  "31": "Memory Layout",
+  "30": "AGENTS.md",
   "32": "Repo Hard Constraints",
   "33": "Go Testing Guide",
   "34": "Session Store",
@@ -37,6 +39,7 @@
   "38": "novel-logic.test.js",
   "39": "UI Critique 2026-07-26A",
   "40": "UI Critique 2026-07-26B",
+  "41": "sessions_test.go",
   "43": "Issue Tracker & Triage",
   "44": "Ticket Workflow",
   "45": "Go Perf Alert Rules",
@@ -146,22 +149,11 @@
   "150": "Reviewer Subagent (opencode)",
   "151": "Finding Severity Rubric",
   "152": "Spec Compliance Review",
+  "158": "T",
   "161": "Why Use samber/oops",
   "162": "singleflight Cache Stampede Prevention",
   "163": "Struct Field Alignment",
   "164": "testing/synctest Deterministic Goroutine Testing",
-  "165": "API Package (Bookmark JSON Handlers)",
-  "166": "Cover Acquisition & Serving Pipeline",
-  "167": "Backend AGENTS.md Guidance",
-  "168": "HTTP Middleware (Auth/Gzip/CORS)",
-  "169": "Latest Package (Site Parsers & Poller)",
-  "170": "Latest-Chapter Poller",
-  "171": "Main Composition Root",
-  "172": "Migration-Owned Schema",
-  "173": "Session Package (Cookie Signing & Rate Limit)",
-  "174": "updated_at List-Order Rule",
-  "175": "Userscript Package (Serving Handler)",
-  "176": "AGENTS.md",
   "177": "Backend CLAUDE.md Guidance",
   "178": "Graphify Knowledge Graph (graphify-out/)",
   "179": "CLAUDE.md (Symlink to AGENTS.md)",
@@ -226,10 +218,6 @@
   "259": "Dark-First Design Constraint",
   "260": "Discord Guild Membership",
   "261": "Reader Isolation Invariant",
-  "268": "Browser Unit Redeploy",
-  "269": "pg_dump Hot Backup",
-  "270": "Redeploy Runbook",
-  "271": "Rollback Strategy",
   "273": "AGENTS.md",
   "279": "Userscript CLAUDE guidance"
 }