Add primary display indicator, custom accent color picker, restart script

- Detect primary monitor via Windows EnumDisplayMonitors API and show badge
- Expand accent color picker with 9 presets and custom color input
- Auto-generate hover color for custom accent colors
- Re-render accent swatches on locale change for proper i18n
- Replace restart-server.bat with PowerShell restart-server.ps1

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

media_server/static/locales/en.json

@@ -10,6 +10,7 @@
   "auth.cleared": "Token cleared. Please enter a new token.",
   "auth.required": "Please enter a token",
   "player.theme": "Toggle theme",
+  "accent.custom": "Custom",
   "player.locale": "Change language",
   "player.previous": "Previous",
   "player.play": "Play/Pause",
@@ -128,6 +129,7 @@
   "display.no_monitors": "No monitors detected",
   "display.power_on": "Turn on",
   "display.power_off": "Turn off",
+  "display.primary": "Primary",
   "browser.title": "Media Browser",
   "browser.home": "Home",
   "browser.manage_folders": "Manage Folders",