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/stores/useSessionStore.ts

@@ -98,7 +98,7 @@ export const useSessionStore = create<SessionStore>()(
             sessionAgentEditModes: new Map(),
             abortPromptSessionId: null,
             abortPromptExpiresAt: null,
-            sessionActivityPhase: new Map(),
+            sessionStatus: new Map(),
             userSummaryTitles: new Map(),
             pendingInputText: null,
             newSessionDraft: { open: true, directoryOverride: null, parentID: null },
@@ -315,19 +315,11 @@ export const useSessionStore = create<SessionStore>()(
                     const draft = get().newSessionDraft;
                     const trimmedAgent = typeof agent === 'string' && agent.trim().length > 0 ? agent.trim() : undefined;
 
-                    const setBusyPhase = (sessionId: string) => {
+                    const setStatus = (sessionId: string, type: 'idle' | 'busy') => {
                         set((state) => {
-                            const next = new Map(state.sessionActivityPhase ?? new Map());
-                            next.set(sessionId, 'busy');
-                            return { sessionActivityPhase: next };
-                        });
-                    };
-
-                    const setIdlePhase = (sessionId: string) => {
-                        set((state) => {
-                            const next = new Map(state.sessionActivityPhase ?? new Map());
-                            next.set(sessionId, 'idle');
-                            return { sessionActivityPhase: next };
+                            const next = new Map(state.sessionStatus ?? new Map());
+                            next.set(sessionId, { type });
+                            return { sessionStatus: next };
                         });
                     };
 
@@ -391,14 +383,14 @@ export const useSessionStore = create<SessionStore>()(
                         }
 
                         get().closeNewSessionDraft();
-                        setBusyPhase(created.id);
+                        setStatus(created.id, 'busy');
 
                         try {
                             return await useMessageStore
                                 .getState()
                                 .sendMessage(content, providerID, modelID, effectiveDraftAgent, created.id, attachments, agentMentionName, additionalParts, variant);
                         } catch (error) {
-                            setIdlePhase(created.id);
+                            setStatus(created.id, 'idle');
                             throw error;
                         }
                     }
@@ -429,14 +421,14 @@ export const useSessionStore = create<SessionStore>()(
                     }
  
                     if (currentSessionId) {
-                        setBusyPhase(currentSessionId);
+                        setStatus(currentSessionId, 'busy');
                     }
 
                     try {
                         return await useMessageStore.getState().sendMessage(content, providerID, modelID, effectiveAgent, currentSessionId || undefined, attachments, agentMentionName, additionalParts, variant);
                     } catch (error) {
                         if (currentSessionId) {
-                            setIdlePhase(currentSessionId);
+                            setStatus(currentSessionId, 'idle');
                         }
                         throw error;
                     }
@@ -504,9 +496,9 @@ export const useSessionStore = create<SessionStore>()(
                 updateViewportAnchor: (sessionId: string, anchor: number) => useMessageStore.getState().updateViewportAnchor(sessionId, anchor),
                 trimToViewportWindow: (sessionId: string, targetSize?: number) => {
                     const currentSessionId = useSessionManagementStore.getState().currentSessionId;
-                    // Skip trimming for sessions in active phase (busy/cooldown)
-                    const phase = get().sessionActivityPhase?.get(sessionId);
-                    if (phase === 'busy' || phase === 'cooldown') {
+                    // Skip trimming while session is working (busy/retry)
+                    const status = get().sessionStatus?.get(sessionId);
+                    if (status?.type === 'busy' || status?.type === 'retry') {
                         return;
                     }
                     return useMessageStore.getState().trimToViewportWindow(sessionId, targetSize, currentSessionId || undefined);