feat: add permission-denied dialog for macOS network/mic access

When macOS denies network access (PermissionDenied), show a localized
dialog explaining how to grant permission in System Settings, with
an 'Open System Settings' button that opens directly to the Local
Network privacy pane.

Also adds author info (Edison Jwa) to About dialog and moves
diagnostics button from AppBar into About dialog.

apps/chanora_flutter/lib/l10n/app_en.arb

@@ -22,6 +22,7 @@
   "@aboutVersion": {
     "placeholders": { "version": { "type": "String" } }
   },
+  "aboutAuthor": "Author: Edison Jwa",
   "aboutNonAffiliation": "Chanora is independent and is not affiliated with, endorsed by, sponsored by, or officially associated with TeamSpeak.",
   "aboutLicenseHeading": "License",
   "aboutLicenseBody": "Chanora is dual-licensed under the Apache License, Version 2.0 or the MIT License, at your option. The full license texts ship as LICENSE-APACHE and LICENSE-MIT at the repository root.",
@@ -154,5 +155,11 @@
     "placeholders": {
       "message": { "type": "String" }
     }
-  }
+  },
+  "networkPermissionTitle": "Network Permission Required",
+  "networkPermissionBody": "Chanora needs permission to access the network. On macOS, go to System Settings → Privacy & Security → Local Network and enable Chanora, then try again.",
+  "networkPermissionOpenSettings": "Open System Settings",
+  "microphonePermissionTitle": "Microphone Permission Required",
+  "microphonePermissionBody": "Chanora needs permission to access the microphone. On macOS, go to System Settings → Privacy & Security → Microphone and enable Chanora.",
+  "permissionDenied": "Permission Denied"
 }