feat(android): Google OAuth via system browser + deep link for Android

Background: Google blocks OAuth in embedded WebView (403 disallowed_useragent).
Solution: open Google login in the Android system browser, then deep-link
back to the Tauri app via custom scheme after callback.

Changes:
- Tauri: add tauri-plugin-opener + tauri-plugin-deep-link to Cargo.toml
- Tauri: register plugins in lib.rs, add capabilities
- Web: auth-form.tsx Google button uses openUrl() via @tauri-apps/plugin-opener
  on Tauri (opens in system browser), falls back to window.location.href
- Web: add lib/tauri.ts for isTauri() detection + lazy opens
- API: /auth/google accepts ?platform=tauri → encodes into OAuth state param
- API: /auth/google/callback decodes state → if tauri, renders HTML page
  that deep-links back via zeavisedu:// scheme; if web, 302 redirect
- Android: patch script adds deep link intent filter for zeavisedu:// scheme

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

package.json

@@ -13,5 +13,9 @@
   "workspaces": [
     "apps/*",
     "packages/*"
-  ]
+  ],
+  "dependencies": {
+    "@tauri-apps/plugin-deep-link": "2.4.9",
+    "@tauri-apps/plugin-opener": "2.5.4"
+  }
 }