feat(audio): Visual×Audio Python contract — resolver, controls, state, API

- player/audio.py: pure resolve_visual / resolve_audio_url / resolve_audio (§4/§6)
- retire player/content.py (7-way table) + its test
- player/controls.py: serial contract content -> visual + audio
- player/state.py: Playback carries video:bool + audio_source:str
- simulator/app.py: /api/alteration validates visual+audio, returns render.video
  + server-resolved render.audio.url from altitude_index; NOISE_URL constant
- tests reframed; full suite 285 passed, 2 skipped

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

player/state.py

@@ -20,7 +20,7 @@ from typing import Callable, Optional
 
 from hef.selection import Coordinate
 from player.alteration import RenderPlan, plan_alteration
-from player.content import ContentResolution, resolve_content
+from player.audio import resolve_visual
 from player.controls import Controls
 
 
@@ -34,11 +34,14 @@ class TransitionKind:
 
 @dataclass(frozen=True)
 class Playback:
-    """What should currently be playing."""
+    """What should currently be playing. Visual and audio are orthogonal (audio
+    spec §2): `video` is whether the projector shows footage, `audio_source` is
+    the independent audio dial (off / soundtrack / white_noise)."""
 
     clip_id: Optional[str]            # None = black walls
     plan: Optional[RenderPlan]        # None when black
-    content: ContentResolution
+    video: bool                       # whether footage is shown (Visual on/off)
+    audio_source: str                 # the Audio dial source (off/soundtrack/white_noise)
     volume: int
     brightness: int
 
@@ -58,7 +61,8 @@ def _first(library):
 _BLACK = Playback(
     clip_id=None,
     plan=None,
-    content=ContentResolution("none", False),
+    video=False,
+    audio_source="off",
     volume=0,
     brightness=0,
 )
@@ -78,12 +82,13 @@ class Player:
         self._current = _BLACK
 
     def _resolve(self, controls: Controls) -> Playback:
-        content = resolve_content(controls.content)
-        if not content.video:
+        video = resolve_visual(controls.visual)
+        if not video:
             return Playback(
                 clip_id=None,
                 plan=None,
-                content=content,
+                video=False,
+                audio_source=controls.audio,
                 volume=controls.volume,
                 brightness=controls.brightness,
             )
@@ -92,7 +97,8 @@ class Player:
         return Playback(
             clip_id=clip.id,
             plan=plan_alteration(coord),
-            content=content,
+            video=True,
+            audio_source=controls.audio,
             volume=controls.volume,
             brightness=controls.brightness,
         )