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/useConfigStore.ts

@@ -8,7 +8,6 @@ import type { ModelMetadata } from "@/types";
 import { getSafeStorage } from "./utils/safeStorage";
 import type { SessionStore } from "./types/sessionTypes";
 import { filterVisibleAgents } from "./useAgentsStore";
-import { isDesktopRuntime, getDesktopSettings } from "@/lib/desktop";
 import { getRegisteredRuntimeAPIs } from "@/contexts/runtimeAPIRegistry";
 import { updateDesktopSettings } from "@/lib/persistence";
 import { useDirectoryStore } from "@/stores/useDirectoryStore";
@@ -30,19 +29,7 @@ interface OpenChamberDefaults {
 
 const fetchOpenChamberDefaults = async (): Promise<OpenChamberDefaults> => {
     try {
-        // 1. Desktop runtime (Tauri)
-        if (isDesktopRuntime()) {
-            const settings = await getDesktopSettings();
-            return {
-                defaultModel: settings?.defaultModel,
-                defaultVariant: settings?.defaultVariant,
-                defaultAgent: settings?.defaultAgent,
-                autoCreateWorktree: settings?.autoCreateWorktree,
-                gitmojiEnabled: settings?.gitmojiEnabled,
-            };
-        }
-
-        // 2. Runtime settings API (VSCode)
+        // 1. Runtime settings API (VSCode)
         const runtimeSettings = getRegisteredRuntimeAPIs()?.settings;
         if (runtimeSettings) {
             try {
@@ -67,7 +54,7 @@ const fetchOpenChamberDefaults = async (): Promise<OpenChamberDefaults> => {
             }
         }
 
-        // 3. Fetch API (Web)
+        // 2. Fetch API (Web/server)
         const response = await fetch('/api/config/settings', {
             method: 'GET',
             headers: { Accept: 'application/json' },