Fix Story 12: Claude API key storage now working

- Fixed silent API key save failure by switching from keyring to Tauri store
- Removed keyring dependency (didn't work in macOS dev mode for unsigned apps)
- Implemented reliable cross-platform storage using tauri-plugin-store
- Added pendingMessageRef to preserve user message during API key dialog flow
- Refactored sendMessage to accept optional message parameter for retry
- Removed all debug logging and test code
- Removed unused entitlements.plist and macOS config
- API key now persists correctly between sessions
- Auto-retry after saving key works properly

Story 12 complete and archived.

src-tauri/Cargo.lock

@@ -1999,16 +1999,6 @@ dependencies = [
  "unicode-segmentation",
 ]
 
-[[package]]
-name = "keyring"
-version = "3.6.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "eebcc3aff044e5944a8fbaf69eb277d11986064cba30c468730e8b9909fb551c"
-dependencies = [
- "log",
- "zeroize",
-]
-
 [[package]]
 name = "kuchikiki"
 version = "0.8.8-speedreader"
@@ -2098,7 +2088,6 @@ dependencies = [
  "eventsource-stream",
  "futures",
  "ignore",
- "keyring",
  "reqwest",
  "serde",
  "serde_json",