Add per-target protocol selection (DDP/HTTP) and reorganize target editor

- Add protocol field (ddp/http) to storage, API schemas, routes, processor
- WledTargetProcessor passes protocol to create_led_client(use_ddp=...)
- Target editor: protocol dropdown + keepalive in collapsible Specific Settings
- FPS, brightness threshold, adaptive FPS moved to main form area
- Hide Specific Settings section for serial devices (protocol is WLED-only)
- Card badge: show DDP/HTTP for WLED devices, Serial for serial devices

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

server/src/wled_controller/static/locales/en.json

@@ -367,6 +367,7 @@
   "targets.section.devices": "💡 Devices",
   "targets.section.color_strips": "🎞️ Color Strip Sources",
   "targets.section.targets": "⚡ Targets",
+  "targets.section.specific_settings": "Specific Settings",
   "targets.add": "Add Target",
   "targets.edit": "Edit Target",
   "targets.loading": "Loading targets...",
@@ -915,6 +916,9 @@
   "targets.min_brightness_threshold.hint": "Effective output brightness (pixel brightness × device/source brightness) below this value turns LEDs off completely (0 = disabled)",
   "targets.adaptive_fps": "Adaptive FPS:",
   "targets.adaptive_fps.hint": "Automatically reduce send rate when the device becomes unresponsive, and gradually recover when it stabilizes. Recommended for WiFi devices with weak signal.",
+  "targets.protocol": "Protocol:",
+  "targets.protocol.hint": "DDP sends pixels via fast UDP (recommended for most setups). HTTP uses the JSON API — slower but reliable, limited to ~500 LEDs.",
+  "targets.protocol.serial": "Serial",
 
   "search.open": "Search (Ctrl+K)",
   "search.placeholder": "Search entities... (Ctrl+K)",