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/controls.py

@@ -1,20 +1,17 @@
 """Control-panel state: the data shape read from the Arduino over serial.
 
 This is the serial-contract payload shared with sub-project 4 (firmware). It
-models the full panel from design §6/§7: the 7-way content dial, the four
-experience knobs (0..4), and the two intensity levels (volume, brightness).
-The wire framing itself is the separate 3<->4 serial contract; this module is
-the *decoded* form.
+models the full panel from the audio spec §3: a Visual toggle (on/off) + an
+Audio source selector (off/soundtrack/white_noise), the four experience knobs
+(0..4), and the two intensity levels (volume, brightness). The wire framing
+itself is the separate 3<->4 serial contract; this module is the *decoded* form.
 """
 
 from __future__ import annotations
 
 from dataclasses import dataclass, fields
 
-# The seven positions of the content dial (design §6).
-CONTENT_POSITIONS = frozenset(
-    {"off", "white_noise", "music", "audio_track", "video", "music_video", "audio_video"}
-)
+from player.audio import AUDIO_SOURCES, VISUAL_POSITIONS
 
 KNOB_FIELDS = ("left", "right", "dark", "light", "volume", "brightness")
 KNOB_MIN = 0
@@ -27,7 +24,8 @@ class ControlsError(ValueError):
 
 @dataclass(frozen=True)
 class Controls:
-    content: str
+    visual: str
+    audio: str
     left: int
     right: int
     dark: int
@@ -38,10 +36,15 @@ class Controls:
 
 def validate_controls(c: Controls) -> None:
     """Raise ControlsError if the payload is structurally invalid."""
-    if c.content not in CONTENT_POSITIONS:
+    if c.visual not in VISUAL_POSITIONS:
         raise ControlsError(
-            f"invalid content position {c.content!r}; "
-            f"expected one of {sorted(CONTENT_POSITIONS)}"
+            f"invalid visual position {c.visual!r}; "
+            f"expected one of {sorted(VISUAL_POSITIONS)}"
+        )
+    if c.audio not in AUDIO_SOURCES:
+        raise ControlsError(
+            f"invalid audio source {c.audio!r}; "
+            f"expected one of {sorted(AUDIO_SOURCES)}"
         )
     for name in KNOB_FIELDS:
         value = getattr(c, name)