v2: real-time Now Playing cadence + robust long-title BLE writes

Decouple the two data sources that share the BLE link:
- Anthropic usage / rate-limit: still polled every 60s.
- Windows media session: read every 3s and pushed the moment the track or
  play/pause state changes, so a song change reaches the watch in seconds
  instead of at the next 60s poll. The last usage payload is cached and merged
  into each now-playing write, so the firmware always gets one complete JSON
  object and the usage screens never blank between polls.

Fix: long media titles (a 44-char Cyrillic title -> ~256 B once json escapes
each char to \uXXXX) overflowed the ATT MTU, so every write-without-response
failed with E_INVALIDARG and tripped the zombie-link break in a reconnect loop.
Switch the RX write to response=True (WinRT does a reliable long write; the RX
char already advertises WRITE and NimBLE reassembles into its 512 B buffer) and
serialize with ensure_ascii=False so Cyrillic goes as 2-byte UTF-8 instead of
6-byte escapes. Verified on hardware: stable link, writes succeed across the
60s heartbeat.

Firmware: only re-set the Now Playing labels when the track / state actually
changed, so the faster cadence does not restart the circular title-scroll
animation on every (often identical) payload.

requirements-windows.txt: add winrt-Windows.Media[.Control]. Phase 5 imports
them but they were never declared, so now-playing silently degraded to
"nothing playing" on a fresh machine.

tests: fix two stale poll_api assertions that expected an "ok" key poll_api has
not emitted since that flag moved to the caller (connect_and_run).

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

daemon/requirements-windows.txt

@@ -4,3 +4,8 @@ bleak
 httpx
 pystray
 Pillow
+# Now Playing (Phase 5): read the Windows "now playing" media session (SMTC).
+# bleak already pulls winrt-runtime + the Bluetooth projections; these add the
+# media-control projection. pip resolves them to the same winrt-runtime as bleak.
+winrt-Windows.Media
+winrt-Windows.Media.Control