refactor(api): complete fastapi migration and related features

Finish native FastAPI controllers, drop vendored microdot, and add
Wi-Fi driver runtime, beat SSE, simulated BPM, sequence playback
improvements, bridge ESP-NOW sources, UI updates, and tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_audio_sse.py

@@ -0,0 +1,34 @@
+"""Server-sent events for audio/beat status."""
+
+import asyncio
+import json
+
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_initial_sse_line_includes_status(monkeypatch):
+    from util import beat_status_broadcaster as bsb
+
+    bsb.configure(
+        loop=asyncio.get_running_loop(),
+        status_builder=lambda: {"bpm_simulated": True, "beat_seq": 3},
+    )
+    line = await bsb.initial_sse_line()
+    assert line.startswith("data: ")
+    payload = json.loads(line[6:])
+    assert payload["type"] == "status"
+    assert payload["status"]["beat_seq"] == 3
+
+
+def test_audio_events_sse_first_chunk(server):
+    c = server["client"]
+    with c.stream("GET", "/api/audio/events") as resp:
+        assert resp.status_code == 200
+        assert "text/event-stream" in resp.headers.get("content-type", "")
+        chunk = next(resp.iter_bytes())
+    text = chunk.decode("utf-8")
+    assert text.startswith("data: ")
+    payload = json.loads(text.strip().removeprefix("data: "))
+    assert payload.get("type") == "status"
+    assert "bpm_simulated" in payload.get("status", {})