Add Windows GUI

- mediahive/winmain.py: pywebview launcher with threaded uvicorn backend,
- scripts/winbuild.py: build script — downloads ffmpeg, runs PyInstaller, makes zip
- mediahive/config.py: TOML config persistence in %APPDATA%/mediahive/
- server.py: POST /api/change-folder switches media root
- showreel.py: suppress console windows for ffmpeg subprocesses on Windows
- protocol.py: add ChangeFolderRequest struct

pyproject.toml

@@ -13,6 +13,7 @@ dependencies = [
     "httpx[http2]>=0.28.1",
     "msgspec>=0.19",
     "parse-torrent-title>=2.8.1",
+    "tomli-w>=1.2.0",
     "uvicorn[standard]>=0.40.0",
 ]
 
@@ -37,6 +38,13 @@ package = true
 [tool.uv.sources]
 parse-torrent-title = { git = "https://github.com/platelminto/parse-torrent-title.git" }
 
+[project.optional-dependencies]
+gui = [
+    "pywebview>=6.2.1",
+    "pythonnet>=3.1.0rc0; platform_system == 'Windows' and python_version >= '3.14'",
+    "pyinstaller>=6.0",
+]
+
 [dependency-groups]
 dev = [
     "httpx>=0.28.1",