fix(ios): unblock iOS Debug builds + regenerate FRB for file transfer API (#41)

* fix(ios): preserve Silero VAD symbols in Flutter Debug builds

Flutter Debug builds split user code into a sibling Chanora.debug.dylib
alongside a minimal launcher executable; the six @_cdecl symbols
chanora_silero_vad_* land in the dylib, not the main binary. Two
problems were hiding behind that:

1. Debug.xcconfig only carried -exported_symbol flags, missing the
   load-bearing -u force-undefined flags Release.xcconfig already had.
   Without -u, the linker dropped the Swift @_cdecl symbols (no Swift
   caller exists) before -exported_symbol could re-export them, so the
   dylib shipped without the VAD entry points.

2. verify_silero_exports.sh inspected only ${EXECUTABLE_PATH}, which in
   Debug builds is the launcher stub. Even with the symbols correctly
   landing in the debug dylib, the script falsely reported them missing.

Mirror Release.xcconfig's -u + -exported_symbol pair in Debug.xcconfig
and teach the verify script to prefer Chanora.debug.dylib when it sits
next to the launcher. Release builds are unaffected (single fat binary
remains the inspected target).

* build(flutter): regenerate FRB bindings for file transfer API

Run flutter_rust_bridge_codegen against the post-PR-#40 chanora_bridge
to emit typed Dart bindings for initCache, downloadAvatar, downloadIcon,
clearFileCache, and fileCacheSize. Replaces the dynamic-cast +
NoSuchMethodError-swallowing shims that lib/src/rust/api.dart shipped
as a pre-regen safety net.

Functional change: downloadAvatar/downloadIcon now return Uint8List?
(was List<int>?) directly through the typed dispatch table. Existing
consumers stay source-compatible because Uint8List extends List<int>;
no call sites needed updates.

* fix(ios): set ITSAppUsesNonExemptEncryption to false

App uses only standard/exempt encryption (HTTPS, system-provided crypto);
declaring exempt status removes the App Store export-compliance prompt
at every TestFlight/release upload.

apps/chanora_flutter/lib/src/rust/api.dart

@@ -226,40 +226,28 @@ String exportDiagnostics() => RustLib.instance.api.crateApiExportDiagnostics();
 Future<void> initStorage({required String dir}) =>
     RustLib.instance.api.crateApiInitStorage(dir: dir);
 
-/// Wire the blob cache to a platform-private cache directory.
-Future<void> initCache({required String dir}) {
-  final api = RustLib.instance.api as dynamic;
-  try {
-    return api.crateApiInitCache(dir: dir) as Future<void>;
-  } on NoSuchMethodError {
-    return Future.value();
-  }
-}
+/// Configure the bridge blob cache root.
+Future<void> initCache({required String dir}) =>
+    RustLib.instance.api.crateApiInitCache(dir: dir);
 
-/// Return an avatar from cache when present; otherwise download it.
-Future<List<int>?> downloadAvatar({
+/// Resolve avatar bytes through the bridge.
+Future<Uint8List?> downloadAvatar({
   required String avatarHash,
   required String clientUid,
-}) {
-  final api = RustLib.instance.api as dynamic;
-  try {
-    return api.crateApiDownloadAvatar(
-      avatarHash: avatarHash,
-      clientUid: clientUid,
-    ) as Future<List<int>?>;
-  } on NoSuchMethodError {
-    return Future.value();
-  }
-}
+}) => RustLib.instance.api.crateApiDownloadAvatar(
+  avatarHash: avatarHash,
+  clientUid: clientUid,
+);
 
-Future<List<int>?> downloadIcon({required BigInt iconId}) {
-  final api = RustLib.instance.api as dynamic;
-  try {
-    return api.crateApiDownloadIcon(iconId: iconId) as Future<List<int>?>;
-  } on NoSuchMethodError {
-    return Future.value();
-  }
-}
+/// Resolve icon bytes through the bridge.
+Future<Uint8List?> downloadIcon({required BigInt iconId}) =>
+    RustLib.instance.api.crateApiDownloadIcon(iconId: iconId);
+
+/// Purge cached protocol-owned assets.
+Future<void> clearFileCache() => RustLib.instance.api.crateApiClearFileCache();
+
+/// Report the configured file-cache size.
+Future<BigInt> fileCacheSize() => RustLib.instance.api.crateApiFileCacheSize();
 
 /// List persisted bookmarks.
 Future<List<BridgeBookmark>> listBookmarks() =>