Add standalone Castle accounting app

New standalone app at castle.html with its own Vite config, app shell,
and bottom nav (Record, Transactions, Balance, Wallet, Settings). Reuses
existing expenses and wallet modules with base module for a focused
accounting experience.

Features:
- Expense submission via existing AddExpense dialog
- Income submission placeholder (feature-flagged, pending backend)
- Balance page with pending expense tracking
- Expense drafts with receipt photo upload and BTC price snapshots
- Cross-subdomain auth token relay via ?token= URL parameter
- i18n support (en/fr/es)
- PWA with offline support

Also adds token relay to activities-app for consistent cross-app auth.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -12,6 +12,9 @@
     "dev:activities": "vite --host --config vite.activities.config.ts",
     "build:activities": "vue-tsc -b && vite build --config vite.activities.config.ts",
     "preview:activities": "vite preview --host --config vite.activities.config.ts",
+    "dev:castle": "vite --host --config vite.castle.config.ts",
+    "build:castle": "vue-tsc -b && vite build --config vite.castle.config.ts",
+    "preview:castle": "vite preview --host --config vite.castle.config.ts",
     "electron:dev": "concurrently \"vite --host\" \"electron-forge start\"",
     "electron:build": "vue-tsc -b && vite build && electron-builder",
     "electron:package": "electron-builder",