Add comix.to and kagane.to support (#13)

Tracks read progress on comix.to and kagane.to alongside asura and demonic, in both the userscript and the backend.

Implements `docs/superpowers/plans/2026-08-03-comix-kagane-support.md`.

## Userscript

- `comix` adapter — `/title/<id>-<slug>`; only the id prefix is identity (the slug follows the title). No `og:image`, so the cover is matched by `alt`.
- `kagane` adapter — reader URLs are uuids with no chapter number, so it comes out of `og:title`; anchor scanning is structurally impossible, replaced by `latestChapterFromApi` against kagane's same-origin JSON API.
- `seriesId` threaded through `latestChapterFromAnchors` so comix can scope its scan to its own series and a recommendation strip cannot win the maximum.
- `@match` for both hosts, panel chips, v1.6.0.

## Backend

- `latestChapterFrom` cases: comix parses the SSR JSON state blob (`latestChapterUrl`, scoped to the series id); kagane parses API JSON (`chapter_no`).
- Poller allowlist extended; `Poller.BrowserFetch` with `fetcherFor(site)` routes kagane to a browser fetcher. Nil means kagane is not polled at all — never a fallback to the TLS fetcher, which would only ever retrieve a challenge page.
- `BrowserFetcher`: chromedp against a `headless-shell` sidecar. kagane sits behind a Cloudflare JS challenge that no TLS fingerprint clears, and the request is made inside the page rather than by replaying `cf_clearance`.
- `BROWSER_WS_URL` wiring, sidecar in both compose files (no `ports:`, dedicated non-external network), Dockerfile on `golang:1.26-alpine` — chromedp requires go 1.26.
- Web UI `--comix` / `--kagane` tokens in both colour branches.

## Notes for review

- `series_url` is client-supplied and a headless browser is a strong SSRF primitive, so kagane's host is pinned twice: in `fetchableSeriesURL` and again in `kaganeAPIURL`.
- Three chained defects found during verification made the browser path dead under Compose (sidecar flag collision, Chrome's Host-header DNS-rebinding check, the wrong chromedp option). Fixed; the compose comments record the wrong configurations too, so they don't get "simplified" back.
- `ALLOWED_ORIGINS` now includes both new origins. Without it every write from comix/kagane silently fails CORS preflight, parks in the retry queue, and drops at the cap.

## Verification

221 backend tests, 32 userscript tests, static `CGO_ENABLED=0` build, both compose configs.

Two gaps, both real:

1. The userscript on live pages via Violentmonkey needs a human browser profile — not run. Check: comix series page (title/cover, no chapter), comix chapter page (records the number; an *older* chapter must not regress it), comix SPA navigation without reload, kagane series page (og:image cover), kagane reader (number from `og:title`), both chips opening the right sites.
2. The kagane browser path has not completed end-to-end anywhere. Dial/navigate/fetch is confirmed, but Cloudflare 403'd headless-shell's Chrome on every attempt from the dev sandbox, and comix's poll-through-Docker was blocked by that environment's TLS interception. Both environment-dependent rather than branch defects — the first real deploy is the actual verification.

Reviewed-on: #13
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

README.md

@@ -1,8 +1,9 @@
 # Manga Bookmark
 
-Track manga read-progress on **asurascans.com** (a.k.a. asuracomic.net) and
-**demonicscans.org** from a phone (Bromite / mobile Chromium), synced to a
-self-hosted Go backend so bookmarks unify across both sites and all devices.
+Track manga read-progress on **asurascans.com** (a.k.a. asuracomic.net),
+**demonicscans.org**, **comix.to**, and **kagane.to** from a phone (Bromite /
+mobile Chromium), synced to a self-hosted Go backend so bookmarks unify across
+all four sites and all devices.
 
 Two parts:
 
@@ -25,9 +26,10 @@ Bromite userscript (isolated world, Shadow DOM UI, localStorage cache)
 | Var | Default | Notes |
 |-----|---------|-------|
 | `API_TOKEN` | *(required)* | Bearer token shared with the userscript. |
-| `ALLOWED_ORIGINS` | Asura + Demonic origins | Comma-separated CORS allowlist. |
+| `ALLOWED_ORIGINS` | Asura + Demonic + Comix + Kagane origins | Comma-separated CORS allowlist. |
 | `DB_PATH` | `/data/bookmarks.db` | SQLite file location. |
 | `PORT` | `8080` | Plain HTTP; TLS terminated by the proxy. |
+| `BROWSER_WS_URL` | `ws://172.28.0.10:9222` | Headless-shell CDP endpoint used to poll Kagane past its JS challenge. Must be an IP or `localhost` — Chrome's DevTools handler 500s any other Host header. |
 
 ### Endpoints
 
@@ -39,8 +41,9 @@ Bromite userscript (isolated world, Shadow DOM UI, localStorage cache)
 | `GET` | `/healthz` | none | `200 ok`. |
 | `GET` | `/u/{token}/manga-bookmark.user.js` | token in path | Serves the userscript with an mtime-derived `@version`. |
 
-`key` is `<site>:<series_id>` — e.g. `asura:trash-of-the-counts-family-f886a8af`
-or `demonic:Infinite-Level-Up-in-Murim`. Sync is last-write-wins.
+`key` is `<site>:<series_id>` — e.g. `asura:trash-of-the-counts-family-f886a8af`,
+`demonic:Infinite-Level-Up-in-Murim`, `comix:12345`, or
+`kagane:3fa85f64-5717-4562-b3fc-2c963f66afa6`. Sync is last-write-wins.
 
 `updated_at` orders the bookmark list, so it moves only on real reading
 progress: the server applies its timestamp when the row is new or
@@ -199,6 +202,8 @@ The site adapters key everything off URL regex, with `title`/`cover` from
 |------|-----------|-------------|-------------|
 | **Asura** (`asurascans.com`) | `/comics/<slug-hash>` | `/comics/<slug-hash>/chapter/<n>` | `<slug-hash>` |
 | **Demonic** (`demonicscans.org`) | `/manga/<slug>` | `/title/<slug>/chapter/<n>/<page>` (`chaptered.php?manga=<id>&chapter=<n>` 301s here) | `<slug>` |
+| **Comix** (`comix.to`) | `/title/<id>-<slug>` | `/title/<id>-<slug>/<uploadId>-chapter-<n>` | `<id>` |
+| **Kagane** (`kagane.to`) | `/series/<uuid>` | `/series/<uuid>/reader/<bookUuid>` | `<uuid>` |
 
 Notes:
 - **`asuracomic.net` deep links are dead (re-checked 2026-07-25).** They 301 to