Fix DXcam engine and improve UI: loading spinners, template card gap

DXcam engine overhaul:
- Remove all user-facing config (device_idx, output_idx, output_color)
  since these are auto-resolved or hardcoded to RGB
- Use one-shot grab() mode with retry for reliability
- Lazily create camera per display via _ensure_camera()
- Clear dxcam global factory cache to prevent stale DXGI state

UI improvements:
- Replace "Loading..." text with CSS spinner animations
- Fix template card header gap on default cards (scope padding-right
  to cards with remove button only via :has selector)
- Add auto-restart server rule to CLAUDE.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -66,6 +66,16 @@
 ✅ Claude: [now creates the commit]
 ```
 
+## IMPORTANT: Auto-Restart Server on Code Changes
+
+**Whenever server-side Python code is modified** (any file under `/server/src/`), **automatically restart the server** so the changes take effect immediately. Do NOT wait for the user to ask for a restart.
+
+### Restart procedure
+
+1. Stop the running Python process: `powershell -Command "Get-Process -Name python -ErrorAction SilentlyContinue | Stop-Process -Force"`
+2. Start the server: `powershell -Command "Set-Location 'c:\Users\Alexei\Documents\wled-screen-controller\server'; python -m wled_controller.main"` (run in background)
+3. Wait 3 seconds and check startup logs to confirm it's running
+
 ## Project Structure
 
 This is a monorepo containing: