chore: drop asuracomic.net from the userscript, CORS allowlist and docs (#97)

Closes #96.

## What

Removes every reference that still invites a Reader onto `asuracomic.net`.
The domain's deep links 301 to the `asurascans.com` **root**, discarding the
path (re-checked 2026-07-25), so a page on it never yields a series document
client-side and a stored address on it never yields a series page server-side.
#95 already pinned each Site to one hostname, so the backend rejects such an
address cleanly; this is the cleanup around that.

| File | Change |
|---|---|
| `userscript/manga-bookmark.user.js` | drops the `@match`, narrows the asura adapter to `/(^\|\.)asurascans\.com$/` |
| `userscript/test/logic.test.js` | new test pinning the narrowed host match |
| `.env.example`, `docker-compose.yml` | origin dropped from the `ALLOWED_ORIGINS` default |
| `DEPLOY.md` | same, and the sample list gains the two novel origins it was missing |
| `backend/api_test.go` | CORS fixtures and round-trip seed move to `asurascans.com` |
| `README.md`, `AGENTS.md` | notes say the host is dropped, not "stays matched" |

## Behaviour

- A Reader landing on `asuracomic.net` gets no userscript UI. Previously the
  script loaded and could do nothing useful — the redirect had already
  discarded the path.
- A request whose `Origin` is `https://asuracomic.net` is no longer reflected
  by a deployment using the shipped defaults.
- No backend logic changed: the CORS rule, the address gate and the poller are
  untouched. `AllowedOrigins` is data, not code.

## Security invariant preserved

CORS still reflects `Origin` only when it appears in `ALLOWED_ORIGINS`, with
`GET,PUT,DELETE,OPTIONS` and a `204` preflight — `TestCORSPreflight` and
`TestCORSDisallowedOrigin` still pin both halves, now against a live origin.
This change only removes a value from the allowlist, which is a narrowing.

## Verification

- `go test ./...` — full backend suite green (real Postgres per package).
- `node --test test/*.test.js` — 66/66 green, up one from the new match test.

## Deploy note (does not happen on merge)

The live allowlist comes from the VPS `.env`, not from these defaults, so the
origin must be dropped there in the same deploy. The one-off row repair for any
stored `asuracomic.net` address is in #96.

Reviewed-on: #97
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/api_test.go

@@ -33,7 +33,7 @@ const testCoverBaseURL = "https://bookmarks.test"
 func testConfig() Config {
 	return Config{
 		TokenKey:       testTokenKey,
-		AllowedOrigins: []string{"https://asuracomic.net", "https://demonicscans.org"},
+		AllowedOrigins: []string{"https://asurascans.com", "https://demonicscans.org"},
 		Port:           "8080",
 	}
 }
@@ -169,7 +169,7 @@ func TestAuthAccepted(t *testing.T) {
 func TestCORSPreflight(t *testing.T) {
 	srv := newTestServer(t)
 	req := httptest.NewRequest(http.MethodOptions, "/bookmarks/asura:foo-1", nil)
-	req.Header.Set("Origin", "https://asuracomic.net")
+	req.Header.Set("Origin", "https://asurascans.com")
 	req.Header.Set("Access-Control-Request-Method", "PUT")
 	rr := httptest.NewRecorder()
 	srv.ServeHTTP(rr, req)
@@ -177,7 +177,7 @@ func TestCORSPreflight(t *testing.T) {
 	if rr.Code != http.StatusNoContent {
 		t.Fatalf("preflight status = %d, want 204", rr.Code)
 	}
-	if got := rr.Header().Get("Access-Control-Allow-Origin"); got != "https://asuracomic.net" {
+	if got := rr.Header().Get("Access-Control-Allow-Origin"); got != "https://asurascans.com" {
 		t.Fatalf("Allow-Origin = %q, want reflected origin", got)
 	}
 	if got := rr.Header().Get("Access-Control-Allow-Methods"); got == "" {
@@ -204,11 +204,11 @@ func TestBookmarkRoundTrip(t *testing.T) {
 	key := "asura:solo-leveling-123"
 	in := store.Bookmark{
 		Title:          "Solo Leveling",
-		SeriesURL:      "https://asuracomic.net/series/solo-leveling-123",
-		Cover:          "https://asuracomic.net/cover.jpg",
+		SeriesURL:      "https://asurascans.com/series/solo-leveling-123",
+		Cover:          "https://asurascans.com/cover.jpg",
 		LastChapter:    "Chapter 10",
 		LastChapterNum: 10,
-		LastChapterURL: "https://asuracomic.net/series/solo-leveling-123/chapter/10",
+		LastChapterURL: "https://asurascans.com/series/solo-leveling-123/chapter/10",
 	}
 	body, _ := json.Marshal(in)