Speed up camera source modal with cached enumeration and instant open

Cache camera enumeration results for 30s and limit probe range using
WMI camera count on Windows. Open source modal instantly with a loading
spinner while dropdowns are populated asynchronously.

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

server/src/wled_controller/core/capture_engines/camera_engine.py

@@ -10,6 +10,7 @@ Prerequisites (optional dependency):
 
 import platform
 import sys
+import time
 from typing import Any, Dict, List, Optional
 
 import numpy as np
@@ -66,23 +67,43 @@ def _get_camera_friendly_names() -> Dict[int, str]:
         return {}
 
 
+_camera_cache: Optional[List[Dict[str, Any]]] = None
+_camera_cache_time: float = 0
+_CAMERA_CACHE_TTL = 30.0  # seconds
+
+
 def _enumerate_cameras(backend_name: str = "auto") -> List[Dict[str, Any]]:
     """Probe camera indices and return metadata for each available camera.
 
+    Results are cached for 30 seconds to avoid repeated slow probes.
     Returns a list of dicts: {cv2_index, name, width, height, fps}.
     """
+    global _camera_cache, _camera_cache_time
+
+    now = time.monotonic()
+    if _camera_cache is not None and (now - _camera_cache_time) < _CAMERA_CACHE_TTL:
+        return _camera_cache
+
     try:
         import cv2
     except ImportError:
+        _camera_cache = []
+        _camera_cache_time = now
         return []
 
     backend_id = _cv2_backend_id(backend_name)
     friendly_names = _get_camera_friendly_names()
 
+    # On Windows, WMI tells us how many cameras exist — skip probing
+    # indices beyond that count to avoid slow timeouts.
+    max_probe = _MAX_CAMERA_INDEX
+    if friendly_names:
+        max_probe = min(len(friendly_names) + 1, _MAX_CAMERA_INDEX)
+
     cameras: List[Dict[str, Any]] = []
     sequential_idx = 0
 
-    for i in range(_MAX_CAMERA_INDEX):
+    for i in range(max_probe):
         if backend_id is not None:
             cap = cv2.VideoCapture(i, backend_id)
         else:
@@ -108,6 +129,9 @@ def _enumerate_cameras(backend_name: str = "auto") -> List[Dict[str, Any]]:
         })
         sequential_idx += 1
 
+    _camera_cache = cameras
+    _camera_cache_time = now
+    logger.debug(f"Camera enumeration: found {len(cameras)} camera(s) (probed {max_probe} indices)")
     return cameras