feat(ios): ad-hoc distribution scripts for pre-TestFlight testing

Add scripts/dist-ios-adhoc.sh and scripts/asc_api.py to build an ad-hoc
signed IPA and the OTA web-install files (manifest.plist + index.html)
for sharing the iOS client with registered devices before TestFlight.

- asc_api.py: App Store Connect API helper (ES256 JWT via cryptography,
  urllib) to register device UDIDs and list registered devices.
- dist-ios-adhoc.sh: registers UDIDs, builds the iOS device xcframework
  slice, archives + exports with method=release-testing using
  -allowProvisioningUpdates, and stages the install files into
  dist/ios-adhoc/.
- Document the workflow in clients/apple/README.md; ignore __pycache__.

.gitignore

@@ -51,3 +51,6 @@ clients/apple/Package.resolved
 # Test artifacts: TOFU pin store written by vc_client during headless tests
 # (core/src/core/client.cpp falls back to this relative path when tofu_store_path is unset).
 voicecat_tofu_pins.txt
+
+# Python bytecode cache (e.g. scripts/asc_api.py)
+__pycache__/