Fix IPC stdout corruption, dark window background, overlay timing

- Redirect sys.stdout to stderr in Python sidecar so library print()
  calls don't corrupt the JSON-line IPC stream
- Save real stdout fd for exclusive IPC use via init_ipc()
- Skip non-JSON lines in Rust reader instead of failing with parse error
- Set Tauri window background color to match dark theme (#0a0a23)
- Add inline dark background on html/body to prevent white flash
- Use Svelte tick() to ensure progress overlay renders before invoke
- Improve ProgressOverlay with spinner, better styling, z-index 9999

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

python/voice_to_notes/main.py

@@ -5,7 +5,13 @@ from __future__ import annotations
 import signal
 import sys
 
-from voice_to_notes.ipc.handlers import (
+# CRITICAL: Capture real stdout for IPC *before* importing any ML libraries
+# that might print to stdout and corrupt the JSON-line protocol.
+from voice_to_notes.ipc.protocol import init_ipc
+
+init_ipc()
+
+from voice_to_notes.ipc.handlers import (  # noqa: E402
     HandlerRegistry,
     hardware_detect_handler,
     make_ai_chat_handler,
@@ -15,8 +21,8 @@ from voice_to_notes.ipc.handlers import (
     make_transcribe_handler,
     ping_handler,
 )
-from voice_to_notes.ipc.messages import ready_message
-from voice_to_notes.ipc.protocol import read_message, write_message
+from voice_to_notes.ipc.messages import ready_message  # noqa: E402
+from voice_to_notes.ipc.protocol import read_message, write_message  # noqa: E402
 
 
 def create_registry() -> HandlerRegistry: