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

frontend/src/styles/main.css

@@ -152,6 +152,28 @@ html, body {
   gap: 12px;
 }
 
+.header-settings {
+  display: flex;
+  align-items: center;
+  margin-left: 8px;
+}
+
+.header-settings-btn {
+  background: transparent;
+  border: none;
+  color: var(--text-secondary);
+  cursor: pointer;
+  padding: 6px;
+  border-radius: 4px;
+  display: flex;
+  align-items: center;
+  transition: color var(--transition-fast);
+}
+
+.header-settings-btn:hover {
+  color: var(--text-primary);
+}
+
 .search-input {
   background: rgba(20, 20, 20, 0.9);
   border: 2px solid var(--border-color);