P2 tiny test server on the mac

[RooRoo6080]

Implements the lightweight FastAPI WebSocket tone server (Issue #4 / P2) to allow testing iOS
streaming connections from a local Mac.

Key Changes

• FastAPI WebSocket Server: Added endpoints (/healthz, /v1/session) in handling the full
  session lifecycle (session_start, caption_text, session_error, session_end).
• Tone Backend Stub: Implemented MockToneBackend in tone.py behind a generic backend interface,
  returning simulated tone tags asynchronously without storing audio or blocking captions.
• Resilient Connection Handling: Emits structured session_error frames rather than abruptly
  closing the WebSocket connection on unprocessable input.
• CLI & Logging / Observability: Added a -v/--verbose flag in main.py to stream events to
  stdout and log NDJSON session traces into gitignored logs/.
• Schema Update: Updated schemas/events.schema.json to v1.1.0 (added session_error),
  updated schema validation tests.
  • May require minor changes in other parts of the project, but I believe this logging will be very helpful in the long run. Version changes, but rest of schema stays the same.
• Test Suite: Added unit and integration tests covering CLI invocation, WebSocket flows, mock
  tone emissions, error handling, and file logging (server/tests/test_server.py,
  server/tests/test_cli.py, server/tests/test_observability.py).

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Tl;dr, to test:

1. uv run --directory server python -m app, add --verbose if you'd like
2. Connect to server using Postman, etc: ws://<local-ip-or-localhost>:8000/ws/session?session_id=demo
3. Sample skeleton message to send:

{
    "type": "tone_request",
    "session_id": "demo",
    "schema_version": "1.1",
    "caption_id": "3f1c2a9e-8b7d-4c6e-9a01-2b3c4d5e6f70",
    "t_start": 1.0,
    "t_end": 1.1,
    "sample_rate": 16000,
    "audio_b64": "AAABAAIA"
}