v2 host: portable desktop app (tray + FastAPI + WebView2 panel), unified config, HA control

Fold the Windows tray/daemon into one self-contained Clawdmeter.exe with a
settings UI, and wire the host side of the watch features:

- config.py: single %LOCALAPPDATA%\Clawdmeter\config.json (ha/buttons/settings),
  atomic writes, auto-migration from the old ha_config.json.
- server.py: local FastAPI (127.0.0.1:8723) — GET/PUT /api/config (token masked),
  POST /api/ha/test, GET /api/ha/entities, GET /api/status.
- web/index.html: brand-styled settings panel (Status/HA/Buttons/Settings tabs).
- panel.py: pywebview/WebView2 window, launched as its own process (pywebview and
  pystray both want the main thread); tray "Settings" opens it via --panel.
- daemon: HA command dispatch (toggle/bri/ct), dynamic button labels + index→
  action mapping, watch-battery low warning toast, and the dimmer "dim" snapshot
  (dimreq → light_snapshot of the first entity) so the watch dial seeds from HA.
- clawdmeter.spec / requirements: bundle fastapi+uvicorn+pywebview+webview backend.
- build-exe.ps1: ASCII-only (Windows PowerShell 5.1 mangles em-dashes under cp1251).

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

.gitignore

@@ -30,3 +30,8 @@ __pycache__/
 
 # Local Home Assistant config (holds a secret token - never commit)
 daemon/ha_config.json
+
+# Session scratch — BLE daemon run logs + one-off on-device QA screenshots
+/m3_daemon*.log
+/dimmer_qa.png
+/build-exe.log