feat(#350): pairing login flow with QR scan + manual entry (#421)

* feat(#350): pairing login flow with QR scan + manual entry

Adds PairingCodeEntryScreen with CameraX + ML Kit QR scanning
and manual code entry. The screen parses hermes://connect URIs,
Base64-encoded JSON, and raw token formats, validates via
/api/status, and saves credentials on success.

- New PairingCodeEntryScreen + PairingCodeEntryViewModel
- CameraX 1.4.1 + ML Kit barcode-scanning 17.3.0
- CAMERA permission + proguard rules
- Landing screen Pairing Login button wired correctly

* fix(#350): resolve smart-cast on delegated property for errorMessage

Co-authored-by: Hy4ri <hy4ri@users.noreply.github.com>

* refactor(#421): remove QR scanner from pairing login

- Remove CameraX + ML Kit barcode dependencies
- Drop CAMERA permission and camera feature from manifest
- Strip QrScannerTab, QrCodeScannerView, processFrame composables
- Remove camera permission state/methods from ViewModel
- Purge all QR/camera strings from strings.xml
- Delete ML Kit proguard rules

The pairing login now shows only the manual code entry UI.

---------

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/res/values/strings.xml

@@ -445,6 +445,11 @@
     <string name="landing_action_auth_login">Auth Login</string>
     <string name="landing_action_pairing_login">Pairing Login</string>
 
+    <!-- Pairing Code Entry Screen -->
+    <string name="pairing_code_entry_title">Pairing Login</string>
+    <string name="pairing_code_entry_manual_desc">Paste the pairing string from your Hermes dashboard below.</string>
+    <string name="pairing_code_entry_code_label">Pairing Code</string>
+
     <!-- Loading State -->
     <string name="loading_state_subtitle_default">Loading…</string>
     <string name="loading_state_subtitle_models">Fetching model providers…</string>