refactor(desktop): make Tauri thin shell running web sidecar (#273)

## What / Why
This PR finishes the desktop refactor: the Tauri app is now a thin shell that launches the web server as a sidecar and loads the UI from `http://127.0.0.1:<port>`. All real backend logic lives in `packages/web/server/index.js`; desktop Rust keeps only native integrations (menu/dialog/notifications/updater/deep-link + window chrome).
This unblocks:
- consistent behavior across web/desktop/vscode (single backend)
- simpler desktop maintenance (no duplicated Rust backend)
- host switching between Local + remote instances in desktop
- reliable cold-start behavior on slow machines (VSCode + desktop)
## Key changes
- Desktop sidecar runtime
  - build pipeline to bundle web dist + `openchamber-server` sidecar (`packages/desktop/scripts/build-sidecar.mjs`)
  - robust local port selection (prefer saved/default, fallback to random; persisted in `~/.config/openchamber/settings.json`)
  - improved PATH handling so the sidecar can locate `opencode` CLI (incl `~/.opencode/bin`, overrides, common bins)
  - disable native right-click context menu in production builds (dev keeps it)
- Desktop instance switcher (Tauri-only)
  - header button + modal to add/edit/delete remote hosts, set default, probe status/ping, switch back to Local escape hatch
  - auth gate includes host switcher so you can recover when a remote host is broken/auth-required
  - host list stored desktop-locally (not tied to the currently selected remote server)
- Notifications
  - decision logic moved server-side; desktop notifications emitted via sidecar stdout and shown natively by Tauri
  - prevent double-notifications on desktop Local origin (UI ignores SSE notification when native path is active)
  - restore macOS notification sound
- Updates
  - Tauri updater used only when viewing Local instance in desktop shell (avoid “remote web update” triggering desktop restart)
- Settings persistence & UX polish
  - persist model favorites/recents via `/api/config/settings` (works for web + desktop; not origin-dependent)
  - persist per-project sidebar collapse state in `projects[].sidebarCollapsed` via `/api/config/settings` (with debounce on toggles)
  - macOS header sizing/traffic-lights offsets fixed (marketing macOS major injected from desktop; MultiRun header aligned)
  - VSCode cold-start: keep retrying provider/agent loads after connection to avoid empty UI on slow machines
  - misc lint/type fixes + bun.lock sync
- Desktop bootstrap / resiliency
  - show onboarding screen when OpenCode CLI is missing (desktop Local origin), with retry hook to restart OpenCode after install
## Testing notes
- Desktop (macOS): switch Local <-> remote, set default host, verify auth gate recovery, native notifications (with sound), updater gated to Local
- Web: favorites/recents + per-project collapsed state persist across reload/restart
- VSCode: slow startup no longer results in missing providers/agents/models

packages/ui/src/components/onboarding/OnboardingScreen.tsx

@@ -1,5 +1,6 @@
 import React from 'react';
 import { RiFileCopyLine, RiCheckLine, RiExternalLinkLine } from '@remixicon/react';
+import { isDesktopShell, isTauriShell } from '@/lib/desktop';
 
 const INSTALL_COMMAND = 'curl -fsSL https://opencode.ai/install | bash';
 const POLL_INTERVAL_MS = 3000;
@@ -35,6 +36,7 @@ export function OnboardingScreen({ onCliAvailable }: OnboardingScreenProps) {
   const [copied, setCopied] = React.useState(false);
   const [showHint, setShowHint] = React.useState(false);
   const [isDesktopApp, setIsDesktopApp] = React.useState(false);
+  const [isRetrying, setIsRetrying] = React.useState(false);
 
   React.useEffect(() => {
     const timer = setTimeout(() => setShowHint(true), HINT_DELAY_MS);
@@ -42,7 +44,7 @@ export function OnboardingScreen({ onCliAvailable }: OnboardingScreenProps) {
   }, []);
 
   React.useEffect(() => {
-    setIsDesktopApp(typeof (window as typeof window & { opencodeDesktop?: unknown }).opencodeDesktop !== 'undefined');
+    setIsDesktopApp(isDesktopShell());
   }, []);
 
   const handleDragStart = React.useCallback(async (e: React.MouseEvent) => {
@@ -50,7 +52,7 @@ export function OnboardingScreen({ onCliAvailable }: OnboardingScreenProps) {
       return;
     }
     if (e.button !== 0) return;
-    if (isDesktopApp) {
+    if (isDesktopApp && isTauriShell()) {
       try {
         const { getCurrentWindow } = await import('@tauri-apps/api/window');
         const window = getCurrentWindow();
@@ -66,12 +68,21 @@ export function OnboardingScreen({ onCliAvailable }: OnboardingScreenProps) {
       const response = await fetch('/health');
       if (!response.ok) return false;
       const data = await response.json();
-      return data.cliAvailable === true;
+      return data.openCodeRunning === true || data.isOpenCodeReady === true;
     } catch {
       return false;
     }
   }, []);
 
+  const handleRetry = React.useCallback(async () => {
+    setIsRetrying(true);
+    try {
+      await fetch('/api/config/reload', { method: 'POST' });
+    } finally {
+      setTimeout(() => setIsRetrying(false), 1000);
+    }
+  }, []);
+
   const handleCopy = React.useCallback(async () => {
     try {
       await navigator.clipboard.writeText(INSTALL_COMMAND);
@@ -146,6 +157,17 @@ export function OnboardingScreen({ onCliAvailable }: OnboardingScreenProps) {
         <p className="text-sm text-muted-foreground animate-pulse">
           Waiting for OpenCode installation...
         </p>
+
+        <div className="flex justify-center">
+          <button
+            type="button"
+            onClick={handleRetry}
+            disabled={isRetrying}
+            className="text-sm text-muted-foreground hover:text-foreground transition-colors"
+          >
+            {isRetrying ? 'Retrying…' : 'Retry'}
+          </button>
+        </div>
       </div>
 
       {showHint && (