feat: bindmount userscript and point Violentmonkey at the backend

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

AGENTS.md

@@ -72,6 +72,8 @@ Bromite userscript (isolated world, per-site adapters, localStorage cache)
   (gates browser UI; unset disables it),
   `LATEST_CHAPTER_POLL_ENABLED`/`_COOLDOWN`/`_INTERVAL`/`_BATCH`/`_STAGGER`
   (background latest-chapter poller; defaults on, `1h`/`10m`/`14`/`20s`).
+  `USERSCRIPT_PATH` (file served at `/u/{token}/manga-bookmark.user.js`,
+  default `/userscript/manga-bookmark.user.js`, supplied by a bindmount).
 
 ### Userscript structure (single IIFE, `manga-bookmark.user.js`)