feat: add config profiles

- Add ConfigProfile and ConfigProfileInclude data models with migrations
- Implement profile resolver service with ordered includes and merge rules
- Add profile CRUD API with validation, compatibility, and cycle detection
- Add instance API plumbing for profile selection on create/start/restart
- Add resolved profile preview and default resolution APIs
- Add frontend config profile API client and management UI
- Add launch/restart profile selection UI
- Add backend integration and unit tests (31 passing)

OpenSpec: add-config-profiles
Quality gates: ruff, TypeScript compile, 31 tests passing

apps/web/src/pages/settings.tsx

@@ -9,6 +9,7 @@ type SettingsStatus = "loading" | "ready" | "error";
 const TABS = [
   { label: "General", path: "general" },
   { label: "SSH Keys", path: "ssh-keys" },
+  { label: "Config Profiles", path: "config-profiles" },
 ] as const;
 
 const THEME_OPTIONS = [
@@ -104,7 +105,7 @@ export const SettingsPage = () => {
           <p className="eyebrow">Configuration</p>
           <h1>Settings</h1>
         </div>
-        <p className="muted">General preferences and SSH keys.</p>
+        <p className="muted">General preferences, SSH keys, and config profiles.</p>
       </header>
 
       <nav className="settings-tabs" aria-label="Settings sections">