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>

apps/tauri/scripts/patch-android-manifest.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
-# Patches the generated AndroidManifest.xml to add CAMERA permission.
+# Patches the generated AndroidManifest.xml with:
+# 1. CAMERA permission
+# 2. Deep link intent filter (zeavisedu:// scheme) for Google OAuth return
 # Run after `tauri android init` to apply.
 set -euo pipefail
 
@@ -10,11 +12,34 @@ if [ ! -f "$MANIFEST" ]; then
   exit 1
 fi
 
-if grep -q 'android.permission.CAMERA' "$MANIFEST"; then
-  echo "CAMERA permission already present in AndroidManifest.xml"
-  exit 0
+# ── CAMERA permission ──────────────────────────────────────────────────
+
+if ! grep -q 'android.permission.CAMERA' "$MANIFEST"; then
+  echo "Adding CAMERA permission to AndroidManifest.xml..."
+  sed -i 's|<uses-permission android:name="android.permission.INTERNET" />|<uses-permission android:name="android.permission.INTERNET" />\n    <uses-permission android:name="android.permission.CAMERA" />\n    <uses-feature android:name="android.hardware.camera" android:required="false" />\n    <uses-feature android:name="android.hardware.camera.autofocus" android:required="false" />|' "$MANIFEST"
+else
+  echo "CAMERA permission already present."
 fi
 
-echo "Adding CAMERA permission to AndroidManifest.xml..."
-sed -i 's|<uses-permission android:name="android.permission.INTERNET" />|<uses-permission android:name="android.permission.INTERNET" />\n    <uses-permission android:name="android.permission.CAMERA" />\n    <uses-feature android:name="android.hardware.camera" android:required="false" />\n    <uses-feature android:name="android.hardware.camera.autofocus" android:required="false" />|' "$MANIFEST"
-echo "Done."
+# ── Deep link intent filter ────────────────────────────────────────────
+# Allows the app to receive zeavisedu:// scheme URLs from the system browser
+# (used after Google OAuth completes in external browser on Android)
+
+DEEP_LINK_FILTER='<!-- Deep link for Google OAuth return from system browser -->\
+        <intent-filter android:autoVerify="true">\
+            <action android:name="android.intent.action.VIEW" />\
+            <category android:name="android.intent.category.DEFAULT" />\
+            <category android:name="android.intent.category.BROWSABLE" />\
+            <data android:scheme="zeavisedu" />\
+        </intent-filter>'
+
+if grep -q 'android:scheme="zeavisedu"' "$MANIFEST"; then
+  echo "Deep link intent filter already present."
+else
+  echo "Adding deep link intent filter to AndroidManifest.xml..."
+  # Insert before the closing </activity> tag of MainActivity
+  sed -i "s|</activity>|${DEEP_LINK_FILTER}\n        </activity>|" "$MANIFEST"
+  echo "Deep link intent filter added."
+fi
+
+echo "AndroidManifest patched successfully."