Add Foundry mobile layout with Tauri iOS/Android support

- Add responsive mobile layout with bottom pill tab bar, swipe navigation, and task list as home screen
- Add platform detection (useIsMobile hook) with viewport breakpoint and VITE_MOBILE build flag
- Mobile-optimize settings/billing/account pages (single-column layout with horizontal tabs)
- Add iOS safe area inset handling with 47px minimum padding
- Scaffold Tauri v2 mobile targets (iOS/Android) with platform-gated sidecar and capabilities
- Add notification sound support and mobile build script

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

foundry/packages/backend/src/actors/workspace/app-shell.ts

@@ -245,6 +245,7 @@ async function buildAppSnapshot(c: any, sessionId: string): Promise<FoundryAppSn
         name: session.currentUserName ?? session.currentUserGithubLogin ?? "GitHub user",
         email: session.currentUserEmail ?? "",
         githubLogin: session.currentUserGithubLogin ?? "",
+        avatarUrl: session.currentUserGithubLogin ? `https://github.com/${session.currentUserGithubLogin}.png` : null,
         roleLabel: session.currentUserRoleLabel ?? "GitHub user",
         eligibleOrganizationIds: organizations.map((organization) => organization.id),
       }