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/session/DirectoryTree.tsx

@@ -12,7 +12,6 @@ import { RiAddLine, RiArrowDownSLine, RiArrowRightSLine, RiCheckLine, RiCloseLin
 import { cn, formatPathForDisplay } from '@/lib/utils';
 import { opencodeClient } from '@/lib/opencode/client';
 import { useDeviceInfo } from '@/lib/device';
-import { isDesktopRuntime, getDesktopSettings } from '@/lib/desktop';
 import type { DesktopSettings } from '@/lib/desktop';
 import { updateDesktopSettings } from '@/lib/persistence';
 import { useFileSystemAccess } from '@/hooks/useFileSystemAccess';
@@ -54,7 +53,6 @@ export const DirectoryTree: React.FC<DirectoryTreeProps> = ({
   isRootReady,
   alwaysShowActions = false,
 }) => {
-  const desktopRuntime = React.useMemo(() => isDesktopRuntime(), []);
   const { isMobile } = useDeviceInfo();
   const [directories, setDirectories] = React.useState<DirectoryItem[]>([]);
   const [expandedPaths, setExpandedPaths] = React.useState<Set<string>>(new Set());
@@ -243,22 +241,17 @@ export const DirectoryTree: React.FC<DirectoryTreeProps> = ({
       }
     };
 
-    const loadPinnedDirectories = async () => {
-      try {
-        let pinned: string[] = [];
+        const loadPinnedDirectories = async () => {
+          try {
+            let pinned: string[] = [];
 
-        if (desktopRuntime) {
-          const settings = await getDesktopSettings();
-          pinned = Array.isArray(settings?.pinnedDirectories) ? settings.pinnedDirectories : [];
-        } else {
-          const response = await fetch('/api/config/settings', {
-            method: 'GET',
-            headers: { Accept: 'application/json' },
-          });
-          if (response.ok) {
-            const data = await response.json();
-            pinned = Array.isArray(data?.pinnedDirectories) ? data.pinnedDirectories : [];
-          }
+        const response = await fetch('/api/config/settings', {
+          method: 'GET',
+          headers: { Accept: 'application/json' },
+        });
+        if (response.ok) {
+          const data = await response.json();
+          pinned = Array.isArray(data?.pinnedDirectories) ? data.pinnedDirectories : [];
         }
 
         if (cancelled) {
@@ -287,7 +280,7 @@ export const DirectoryTree: React.FC<DirectoryTreeProps> = ({
       cancelled = true;
       window.removeEventListener('openchamber:settings-synced', handleSettingsSynced);
     };
-  }, [desktopRuntime, stripTrailingSlashes]);
+  }, [stripTrailingSlashes]);
 
   const isInitialPinnedSync = React.useRef(true);