fix: address reader-UI feedback (shorts, search, tags, login, UX)

- Shorts: confirm via youtube.com/shorts/<id> probe (SOCS cookie bypasses the
  consent redirect) instead of a 60s heuristic; concurrent probing, shorts_probed
  flag, scheduled refinement (migration 0005)
- Search: match title + channel name only (descriptions caused noisy results)
- Faceted tag filtering: AND across categories (language AND topic narrows),
  OR within a category; any/all toggle applies to topics
- Language detection: majority vote over individual titles (fixes misdetections
  like multipoleguy -> English; drops bogus Polish/Romanian)
- Login: drop forced consent so returning sign-in is quick (select_account)
- Feed cards: clickable channel name (opens channel), persistent saved badge,
  undo toast on hide, Hidden view to restore; tag chips show counts in tooltip

backend/app/auth.py

@@ -28,13 +28,14 @@ oauth.register(
 
 @router.get("/login")
 async def login(request: Request):
-    # access_type=offline + prompt=consent must be on the authorization URL so Google
-    # returns a refresh_token (required for background sync).
+    # access_type=offline ensures a refresh_token on first authorization. We avoid
+    # prompt=consent so returning users get a quick sign-in; the stored refresh token
+    # is kept when Google doesn't re-issue one (see the callback).
     return await oauth.google.authorize_redirect(
         request,
         settings.oauth_redirect_url,
         access_type="offline",
-        prompt="consent",
+        prompt="select_account",
         include_granted_scopes="true",
     )