Add warm whisper-server backend (no per-dictation model reload)

Each dictation previously spawned whisper-cli with -m, reloading the full
1.5-1.6GB model (+ ~10s Metal init) every single time. This adds a
WhisperServer manager that keeps a whisper-server child process alive with
the model preloaded, so each utterance is a fast local HTTP POST to
/inference (~0.5s) instead of a multi-second cold start.

- Bundles whisper-server alongside whisper-cli (bundle-whisper.sh).
- Server (re)starts on launch and on model change; stops on terminate;
  picks a free loopback port; -nt (plain text) + -sns (fewer hallucinations).
- transcribe() prefers the warm server and falls back to a per-call
  whisper-cli spawn if the server is unavailable.
- Warm-up now starts BEFORE the blocking accessibility prompt so the model
  load overlaps with the user granting permissions.
- Info.plist: NSAllowsLocalNetworking for the loopback HTTP call.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

macos/WhisperDictate.app/Contents/Info.plist

@@ -26,6 +26,11 @@
 	<string>13.0</string>
 	<key>LSUIElement</key>
 	<true/>
+	<key>NSAppTransportSecurity</key>
+	<dict>
+		<key>NSAllowsLocalNetworking</key>
+		<true/>
+	</dict>
 	<key>NSAppleEventsUsageDescription</key>
 	<string>WhisperDictate needs accessibility access to paste transcribed text.</string>
 	<key>NSHighResolutionCapable</key>