Make existing controls real + add robustness pass

Wire up controls that were rendered but inert, expose unused server
actions, and harden the live update path.

Controls now functional:
- File priority dropdowns (Content tab) now persist via new
  setFilePriority server action
- Context menu: Set location, Limit download/upload rate, Set share
  limit (wire setSavePath/setDownLimit/setUpLimit/setRatioLimit)
- Trackers sidebar filter actually filters (snapshot now carries
  per-torrent trackerHosts)

Robustness:
- Grid updates cells in place when row order/columns are unchanged
  (preserves text selection/scroll, no per-second listener re-bind)
- Boot retries until the server responds; SSE drops show a
  "Reconnecting" banner; failed actions/add/delete surface a toast
- Prune selection/detail for torrents that disappear
- Drop Backspace-as-delete (kept Delete)

Cleanup:
- Remove pseudo DHT/PeX/LSD names from the real-tracker host pool in
  mock data (they leaked into announce URLs and the sidebar)
- Remove dead detailTab import/export

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/data.js

@@ -48,7 +48,7 @@ const TAGS = ['archive', 'public', 'private', 'seed-forever', 'hit-and-run', 've
 const TRACKER_HOSTS = [
   'tracker.opentrackr.org:1337', 'open.demonii.com:1337', 'tracker.torrent.eu.org:451',
   'exodus.desync.com:6969', 'tracker.openbittorrent.com:6969', 'private.tracker.lan:2710',
-  'tracker.dler.org:6969', 'open.stealth.si:80', '** [DHT] **', '** [PeX] **', '** [LSD] **',
+  'tracker.dler.org:6969', 'open.stealth.si:80',
 ];
 
 const NAME_TEMPLATES = [