refactor(platforms): retire deviantart end-to-end (#3069)

Executes the 2026-07-05 product decision (FC downloaders = art-dedicated
services only), which removed Twitter/X and Bluesky but left deviantart
fully wired for seven weeks — the half-retired state rule 22 exists to
prevent.

Removed: the PlatformInfo module and its registry entry, the gallery-dl
extractor block, extension_service's artist-page pattern, the extension's
PLATFORMS + PLATFORM_ARTIST_PATTERNS entries, its manifest host permission
and content-script match, the frontend icon/colour/label, and the operator-
facing "supported platforms" list that still advertised it.

Two judgment calls, both recorded in migration 0088:

  * existing `source` rows are DISABLED, not deleted. The row is the only
    record of the artist's DeviantArt URL. Disabling is also required for
    correctness rather than tidiness: with the platform unregistered the
    download path falls through to gallery-dl, which carries its OWN
    deviantart extractor, so an enabled row would have kept downloading
    from a dropped platform.
  * the `credential` row IS deleted — a live session cookie for a site FC
    will never call again.

Adds the invariant whose absence is why manifest.json drifted in the first
place: nothing tied its domain lists back to the platform table. The
extension suite now asserts both directions, plus that no host permission
belongs to an unclaimed domain (`*://*/*` exempted — FC is self-hosted at
an operator-chosen URL the extension cannot enumerate).

Extension version 1.0.10 -> 1.0.11: ci.yml's guard hard-fails a packaged
extension change without a bump. No release is cut — build.yml's
sign-extension job only runs on main.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

extension/lib/platforms.js

@@ -68,16 +68,6 @@ const PLATFORMS = {
     urlPattern: /^https?:\/\/(www\.)?pixiv\.net/,
     note: 'Click to authenticate via OAuth',
   },
-  deviantart: {
-    name: 'DeviantArt',
-    domains: ['.deviantart.com', 'www.deviantart.com', 'deviantart.com'],
-    authType: 'cookies',
-    color: '#05CC47',
-    urlPattern: /^https?:\/\/(www\.)?deviantart\.com/,
-    // DA's logged-in-only endpoints sit behind their internal _napi
-    // namespace which shifts; skipping verify until a stable check
-    // surfaces. Same posture as SubscribeStar.
-  },
 };
 
 /**
@@ -98,7 +88,6 @@ const PLATFORM_ARTIST_PATTERNS = {
   patreon:       /^https?:\/\/(www\.)?patreon\.com\/(?:cw\/|c\/)?(?!(?:home|search|messages|notifications|library|settings|posts)(?:[\/?#]|$))[^/?#]+/i,
   subscribestar: /^https?:\/\/(www\.)?subscribestar\.(com|adult)\/(?!feed$|messages$|library$)[^/?#]+\/?$/i,
   hentaifoundry: /^https?:\/\/(www\.)?hentai-foundry\.com\/user\/[^/?#]+/i,
-  deviantart:    /^https?:\/\/(www\.)?deviantart\.com\/(?!home$|watch\b|tag\b|browse\b)[^/?#]+\/?$/i,
   pixiv:         /^https?:\/\/(www\.)?pixiv\.net\/(en\/)?users\/\d+/i,
 };