feat(nav): full bookmarkable URL model — retire minimalist-URL + Share-view (E4 S2)

The query string is now the source of truth for the current view, so every URL is
bookmarkable/shareable. Reverses the early minimalist-URL rule (user's call).

- urlState: urlWithParams (read-modify-write delta on the live query, each provider
  owns its keys) + clearParams (strip only transient auth params) replace the whole-
  query stripUrlParams; shareUrl deleted; filterParamUpdates helper.
- NavigationProvider: page + ?chan mirrored to the address bar (pushState URL arg;
  history.state mechanics untouched); loadInitialPage resolves deep links
  (?v->plex, ?pl->playlists, filter/?chan->feed, bare->stored landing).
- FeedFiltersProvider: feed filters mirrored to the URL, gated on page===feed.
- useHistorySubview: optional SubviewUrl mapping; PlexBrowse mirrors the sub-view to
  ?v=<kind>:<args> (show/season/info/person/playlist; grid+player stay ephemeral).
- PlaylistsProvider: selected playlist mirrored to ?pl on the Playlists page.
- App: the 5 stripUrlParams calls become targeted clearParams (link/oauth/admin/
  access/verify/reset); the share-link hydrate effect removed.
- Retire the "Share view" feature: Sidebar + SavedViewsWidget buttons + i18n keys.

Browser tab title stays the short module/channel name (document.title untouched) —
the query never leaks into it, per the user's request.

Gate green: typecheck, knip, eslint (0 err), prettier, 247 vitest (urlState.dom.test
+9). No browser-E2E yet (most visual sprint — flagged for the epic-end review).

frontend/src/i18n/locales/en/sidebar.json

@@ -28,9 +28,6 @@
   "reshuffle": "Reshuffle",
   "noMatchingTags": "No matching tags here",
   "manageTags": "Manage",
-  "shareView": "Copy a link to this view",
-  "shareCopied": "View link copied to clipboard",
-  "shareFailed": "Couldn't copy the link",
   "widget": {
     "savedviews": "Saved views",
     "show": "Show",

frontend/src/i18n/locales/en/views.json

@@ -7,8 +7,6 @@
   "apply": "Apply this view",
   "makeDefault": "Set as default (loads on start)",
   "isDefault": "Default view — loads on start",
-  "share": "Copy a link to this view",
-  "shareCopied": "View link copied",
   "rename": "Rename",
   "delete": "Delete",
   "deleteConfirm": "Delete the saved view “{{name}}”?",

frontend/src/i18n/locales/hu/sidebar.json

@@ -28,9 +28,6 @@
   "reshuffle": "Újrakeverés",
   "noMatchingTags": "Nincs ide illő címke",
   "manageTags": "Kezelés",
-  "shareView": "Hivatkozás másolása erre a nézetre",
-  "shareCopied": "Nézet-hivatkozás a vágólapra másolva",
-  "shareFailed": "Nem sikerült a hivatkozás másolása",
   "widget": {
     "savedviews": "Mentett nézetek",
     "show": "Megjelenítés",

frontend/src/i18n/locales/hu/views.json

@@ -7,8 +7,6 @@
   "apply": "Nézet alkalmazása",
   "makeDefault": "Beállítás alapértelmezettként (indításkor betölt)",
   "isDefault": "Alapértelmezett nézet — indításkor betölt",
-  "share": "Hivatkozás másolása a nézethez",
-  "shareCopied": "Nézet hivatkozása a vágólapra másolva",
   "rename": "Átnevezés",
   "delete": "Törlés",
   "deleteConfirm": "Törlöd a(z) „{{name}}” mentett nézetet?",