chore: drop asuracomic.net from the userscript, CORS allowlist and docs (#96)

The old domain's deep links 301 to the asurascans.com root, discarding the
path, so a page on it never yields a series document and a stored address on
it never yields a series page. #94 pinned each Site to one hostname, which
already rejects such an address server-side; this removes the remaining
references so nothing invites a Reader onto the dead host.

Live deploys still carry the origin in their own .env and must drop it there
too - the allowlist is read from the environment, not from these defaults.

README.md

@@ -1,6 +1,6 @@
 # Manga Bookmark
 
-Track manga read-progress on **asurascans.com** (a.k.a. asuracomic.net),
+Track manga read-progress on **asurascans.com**,
 **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.
@@ -274,11 +274,12 @@ the backend acquires, stores and serves every Cover from its own origin
 | **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
-  the `asurascans.com` **root**, discarding the path, at the edge — before the
-  userscript gets a document — so nothing client-side can rescue them. Reach
-  series through `asurascans.com`. The host stays matched in case the redirect
-  starts preserving paths again.
+- **`asuracomic.net` is no longer matched (deep links dead, re-checked
+  2026-07-25).** They 301 to the `asurascans.com` **root**, discarding the path,
+  at the edge — before the userscript gets a document — so nothing client-side
+  can rescue them. The backend rejects stored addresses on that host too, since
+  the poller pins each Site to one hostname. Reach series through
+  `asurascans.com`.
 - Asura `og:title` carries a `Chapter N - Read Online \| Asura Scans` suffix that
   the adapter strips; Demonic chapter `og:title` is `<Title> Chapter N`.
 - Demonic's `<slug>` is identical on `/manga/…` and the canonical `/title/…`