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/scripts/verify_silero_exports.sh

@@ -31,6 +31,18 @@ if [ ! -f "${BINARY}" ]; then
     exit 1
 fi
 
+# Flutter Debug builds split user code into a sibling `<App>.debug.dylib`
+# alongside a tiny launcher executable; the @_cdecl symbols live in the
+# dylib. Release/Profile builds put everything in the main executable.
+# Prefer the dylib when both exist so the check verifies the slice that
+# actually carries the symbols.
+EXECUTABLE_DIR=$(dirname "${BINARY}")
+EXECUTABLE_NAME=$(basename "${BINARY}")
+DEBUG_DYLIB="${EXECUTABLE_DIR}/${EXECUTABLE_NAME}.debug.dylib"
+if [ -f "${DEBUG_DYLIB}" ]; then
+    BINARY="${DEBUG_DYLIB}"
+fi
+
 REQUIRED_SYMBOLS="
 _chanora_silero_vad_create
 _chanora_silero_vad_destroy