Add PWA support and mobile responsive layout

- PWA manifest, service worker (stale-while-revalidate for static assets,
  network-only for API), and app icons for installability
- Root-scoped /manifest.json and /sw.js routes in FastAPI
- New mobile.css with responsive breakpoints at 768/600/400px:
  fixed bottom tab bar on phones, single-column cards, full-screen modals,
  compact header toolbar, touch-friendly targets
- Fix modal-content-wide min-width overflow on small screens
- Update README with Camera, OpenRGB, and PWA features

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

server/src/wled_controller/main.py

@@ -6,7 +6,7 @@ from pathlib import Path
 
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import JSONResponse
+from fastapi.responses import FileResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
 from fastapi.templating import Jinja2Templates
 from starlette.requests import Request
@@ -248,6 +248,26 @@ app.add_middleware(
 # Include API routes
 app.include_router(router)
 
+# PWA: serve manifest and service worker from root scope
+_static_root = Path(__file__).parent / "static"
+
+
+@app.get("/manifest.json", include_in_schema=False)
+async def pwa_manifest():
+    """Serve PWA manifest from root scope."""
+    return FileResponse(_static_root / "manifest.json", media_type="application/manifest+json")
+
+
+@app.get("/sw.js", include_in_schema=False)
+async def pwa_service_worker():
+    """Serve service worker from root scope (controls all pages)."""
+    return FileResponse(
+        _static_root / "sw.js",
+        media_type="application/javascript",
+        headers={"Cache-Control": "no-cache"},
+    )
+
+
 # Mount static files
 static_path = Path(__file__).parent / "static"
 if static_path.exists():