Add ADB-based Android screen capture engine with display picker integration

New scrcpy/ADB capture engine that captures Android device screens over
ADB using screencap polling. Supports USB and WiFi ADB connections with
device auto-discovery. Engine-aware display picker shows Android devices
when scrcpy engine is selected, with inline ADB connect form for WiFi
devices.

Key changes:
- New scrcpy_engine.py using adb screencap polling (~1-2 FPS over WiFi)
- Engine-aware GET /config/displays?engine_type= API
- ADB connect/disconnect API endpoints (POST /adb/connect, /adb/disconnect)
- Display picker supports engine-specific device lists
- Stream/test modals pass engine type to display picker
- Test template handler changed to sync def to prevent event loop blocking
- Restart script merges registry PATH for newly-installed tools
- All engines (including unavailable) shown in engine list with status flag

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

server/src/wled_controller/templates/modals/stream.html

@@ -24,7 +24,7 @@
                         </div>
                         <small class="input-hint" style="display:none" data-i18n="streams.display.hint">Which screen to capture</small>
                         <input type="hidden" id="stream-display-index" value="">
-                        <button type="button" class="btn btn-display-picker" id="stream-display-picker-btn" onclick="openDisplayPicker(onStreamDisplaySelected, document.getElementById('stream-display-index').value)">
+                        <button type="button" class="btn btn-display-picker" id="stream-display-picker-btn" onclick="openDisplayPicker(onStreamDisplaySelected, document.getElementById('stream-display-index').value, document.getElementById('stream-capture-template').selectedOptions[0]?.dataset?.engineType)">
                             <span id="stream-display-picker-label" data-i18n="displays.picker.select">Select display...</span>
                         </button>
                     </div>

server/src/wled_controller/templates/modals/test-template.html

@@ -9,7 +9,7 @@
             <div class="form-group">
                 <label data-i18n="templates.test.display">Display:</label>
                 <input type="hidden" id="test-template-display" value="">
-                <button type="button" class="btn btn-display-picker" id="test-display-picker-btn" onclick="openDisplayPicker(onTestDisplaySelected, document.getElementById('test-template-display').value)">
+                <button type="button" class="btn btn-display-picker" id="test-display-picker-btn" onclick="openDisplayPicker(onTestDisplaySelected, document.getElementById('test-template-display').value, window.currentTestingTemplate?.engine_type)">
                     <span id="test-display-picker-label" data-i18n="displays.picker.select">Select display...</span>
                 </button>
             </div>