ci: add Windows-only build workflow for self-hosted runner

Adds .gitea/workflows/build-windows.yml targeting the org's self-hosted
`windows-latest` runner: sets up Python 3.11, installs the project +
PyInstaller, builds dist/macropad.exe, uploads it as an artifact, and on a
v* tag creates/updates a Gitea release and attaches the exe via the Gitea
API. Runs entirely on Windows (no Linux runner required).

Also declare relay_client + aiohttp as PyInstaller hidden imports so the
relay feature (lazily imported in the GUI) is bundled into the exe.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

macropad.spec

@@ -48,6 +48,9 @@ a = Analysis(
         'netifaces',
         'websockets',
         'multipart',
+        # Relay client (imported lazily in the GUI, so declare explicitly)
+        'relay_client',
+        'aiohttp',
     ],
     hookspath=[],
     hooksconfig={},