Add value source test modal, auto-gain, brightness always-show, shared value streams

- Add real-time value source test: WebSocket endpoint streams get_value() at
  ~20Hz, frontend renders scrolling time-series chart with min/max/current stats
- Add auto-gain for audio value sources: rolling peak normalization with slow
  decay, sensitivity range increased to 0.1-20.0
- Always show brightness overlay on LED preview when brightness source is set
- Refactor ValueStreamManager to shared ref-counted streams (value streams
  produce scalars, not LED-count-dependent, so sharing is correct)
- Simplify acquire/release API: remove consumer_id parameter since streams
  are no longer consumer-dependent

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

server/src/wled_controller/api/routes/value_sources.py

@@ -1,8 +1,10 @@
 """Value source routes: CRUD for value sources."""
 
+import asyncio
+import secrets
 from typing import Optional
 
-from fastapi import APIRouter, Depends, HTTPException, Query
+from fastapi import APIRouter, Depends, HTTPException, Query, WebSocket, WebSocketDisconnect
 
 from wled_controller.api.auth import AuthRequired
 from wled_controller.api.dependencies import (
@@ -10,6 +12,7 @@ from wled_controller.api.dependencies import (
     get_processor_manager,
     get_value_source_store,
 )
+from wled_controller.config import get_config
 from wled_controller.api.schemas.value_sources import (
     ValueSourceCreate,
     ValueSourceListResponse,
@@ -43,6 +46,7 @@ def _to_response(source: ValueSource) -> ValueSourceResponse:
         mode=d.get("mode"),
         sensitivity=d.get("sensitivity"),
         smoothing=d.get("smoothing"),
+        auto_gain=d.get("auto_gain"),
         schedule=d.get("schedule"),
         picture_source_id=d.get("picture_source_id"),
         scene_behavior=d.get("scene_behavior"),
@@ -92,6 +96,7 @@ async def create_value_source(
             schedule=data.schedule,
             picture_source_id=data.picture_source_id,
             scene_behavior=data.scene_behavior,
+            auto_gain=data.auto_gain,
         )
         return _to_response(source)
     except ValueError as e:
@@ -138,6 +143,7 @@ async def update_value_source(
             schedule=data.schedule,
             picture_source_id=data.picture_source_id,
             scene_behavior=data.scene_behavior,
+            auto_gain=data.auto_gain,
         )
         # Hot-reload running value streams
         pm.update_value_source(source_id)
@@ -168,3 +174,68 @@ async def delete_value_source(
         return {"status": "deleted", "id": source_id}
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))
+
+
+# ===== REAL-TIME VALUE SOURCE TEST WEBSOCKET =====
+
+
+@router.websocket("/api/v1/value-sources/{source_id}/test/ws")
+async def test_value_source_ws(
+    websocket: WebSocket,
+    source_id: str,
+    token: str = Query(""),
+):
+    """WebSocket for real-time value source output. Auth via ?token=<api_key>.
+
+    Acquires a ValueStream for the given source, polls get_value() at ~20 Hz,
+    and streams {value: float} JSON to the client.
+    """
+    # Authenticate
+    authenticated = False
+    cfg = get_config()
+    if token and cfg.auth.api_keys:
+        for _label, api_key in cfg.auth.api_keys.items():
+            if secrets.compare_digest(token, api_key):
+                authenticated = True
+                break
+
+    if not authenticated:
+        await websocket.close(code=4001, reason="Unauthorized")
+        return
+
+    # Validate source exists
+    store = get_value_source_store()
+    try:
+        store.get_source(source_id)
+    except ValueError as e:
+        await websocket.close(code=4004, reason=str(e))
+        return
+
+    # Acquire a value stream
+    manager = get_processor_manager()
+    vsm = manager.value_stream_manager
+    if vsm is None:
+        await websocket.close(code=4003, reason="Value stream manager not available")
+        return
+
+    try:
+        stream = vsm.acquire(source_id)
+    except Exception as e:
+        await websocket.close(code=4003, reason=str(e))
+        return
+
+    await websocket.accept()
+    logger.info(f"Value source test WebSocket connected for {source_id}")
+
+    try:
+        while True:
+            value = stream.get_value()
+            await websocket.send_json({"value": round(value, 4)})
+            await asyncio.sleep(0.05)
+    except WebSocketDisconnect:
+        pass
+    except Exception as e:
+        logger.error(f"Value source test WebSocket error for {source_id}: {e}")
+    finally:
+        vsm.release(source_id)
+        logger.info(f"Value source test WebSocket disconnected for {source_id}")