Add min/max value range to audio value sources

Add min_value and max_value fields to AudioValueSource so audio
brightness can be mapped to a configurable range (e.g. silence =
30% brightness floor instead of fully black).

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

server/src/wled_controller/storage/value_source.py

@@ -91,6 +91,8 @@ class ValueSource:
                 mode=data.get("mode") or "rms",
                 sensitivity=float(data.get("sensitivity") or 1.0),
                 smoothing=float(data.get("smoothing") or 0.3),
+                min_value=float(data.get("min_value") or 0.0),
+                max_value=float(data["max_value"]) if data.get("max_value") is not None else 1.0,
             )
 
         if source_type == "adaptive_time":
@@ -167,10 +169,12 @@ class AudioValueSource(ValueSource):
     into a scalar value for brightness modulation.
     """
 
-    audio_source_id: str = ""    # references a MonoAudioSource
+    audio_source_id: str = ""    # references an audio source (mono or multichannel)
     mode: str = "rms"            # rms | peak | beat
     sensitivity: float = 1.0     # gain multiplier (0.1–5.0)
     smoothing: float = 0.3       # temporal smoothing (0.0–1.0)
+    min_value: float = 0.0       # minimum output (0.0–1.0)
+    max_value: float = 1.0       # maximum output (0.0–1.0)
 
     def to_dict(self) -> dict:
         d = super().to_dict()
@@ -178,6 +182,8 @@ class AudioValueSource(ValueSource):
         d["mode"] = self.mode
         d["sensitivity"] = self.sensitivity
         d["smoothing"] = self.smoothing
+        d["min_value"] = self.min_value
+        d["max_value"] = self.max_value
         return d