feat: v2.5.5 — AI Router renamed AI Proxy, reload onto new builds, update no longer spins

AI Proxy (was AI Router):
- server/lib/ai-proxies.js, proxy-apply.js, routes/ai-proxies.js mounted at
  /api/ai-proxies and the old /api/ai-routers; `router` still accepted on the
  start routes; profiles move to <CLAUDE_HOME>/agenthub-proxies/
- dashboard_runs.router renamed in place to proxy: an older build on the same
  DB fails on that column, so dev and prod sharing one DB update together
- a proxy's baseUrl stored as its root (a typed /v1 made /v1/v1/messages);
  Test probes Claude /v1/messages and Codex /v1/responses
- Settings → AI Proxy (/settings/ai-router redirects), ProxyPicker

Updates:
- every tab reloads onto the new UI build when its WebSocket reconnects to a
  server of another version (lib/newBuildReload.ts, once per version)
- Update now stops waiting on a plugin chain that failed or pulled nothing
  (the old server never goes down), and reloads as soon as a new version answers

Also:
- a pane whose command exits at once says so (EPANEEXITED) instead of
  "Command failed: tmux set-option … mouse on"
- the pane drag preview draws where the pane actually lands

client/src/i18n/locales/en/updates.json

@@ -25,6 +25,7 @@
   "releaseUnavailable": "Could not read the latest release from the repository ({{reason}}); fell back to comparing commits.",
   "pluginAutoNote": "This dashboard is installed as a Claude Code plugin. \"Update now\" pulls the new plugin version, reinstalls the runtime, and restarts the server for you — it takes a few minutes. Newly added skills and slash commands only appear in an already-open Claude Code session after you run /reload-plugins there.",
   "pluginUpdating": "Pulling the new plugin version and reinstalling the runtime — this takes a few minutes, the page reloads itself when the new server is up...",
+  "pluginAlreadyCurrent": "No newer plugin version was pulled, so the running dashboard was left as it is.",
   "lastPluginUpdateFailed": "The last plugin update failed at step \"{{step}}\": {{error}} — run /agenthub-update in Claude Code to recover.",
   "restartingShort": "Restarting…",
   "installedTitle": "Version {{version}} is installed but not running",