feat(a2b): audio — wire play-bgm/play-voice, fix BGM addressing

Wire audio end-to-end (OGG plays natively in Godot; no Frida, no decode):
- IHost.PlayBgm/PlayVoice + VM dispatch for play-bgm(0xbf)/play-voice(0xc4).
  Non-Godot hosts no-op them so --selftest + engine 8/8 stay byte-identical.
- GodotAdvHost resolves id->OGG; Main plays via two AudioStreamPlayer nodes
  (BGM looping; voice interrupt-on-new).

Key finding (by-ear, systematic-debugging): the two audio ops use DIFFERENT
addressing — the earlier "unified manifest" assumption was wrong for BGM.
- play-voice -> per-scene manifest files[base+id] (offset 0, same as textures).
  Confirmed by ear; upgraded med->HIGH.
- play-bgm  -> DIRECT LITERAL NAME BGM{id:03d}.OGG, NOT the manifest.
  Real game: play-bgm 5->BGM005, 8->BGM008 (manifest gave +1). Proven by
  play-bgm 0x23->BGM035 (real standalone track; BGM set skips 030-034) that the
  manifest mis-resolved to a graphics entry. Fix is BGM-only:
  ResourceMap.BgmPathById; voices/textures unchanged.

Also: Lily's silence root-caused as correct form-gating (G[0xa57/0xa58/0xa59]),
left unseeded by choice (no dummy state). Added diagnostic
`Age.Cli audio <SCENE.BIN> [0xADDR=VAL ...]`. Corrected opcodes.toml (play-bgm
direct-name, play-voice HIGH) + docs/memory (dropped the bogus unified-manifest
/ Frida-BGM006 claims).

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

docs/opcode-reference.md

@@ -18,14 +18,14 @@
 - **evidence:** confirm via frida
 
 ### 0xbf `play-bgm` (play-bgm, argc 1)
-- **summary:** Play background music by id; id resolves via the SYS4INI section manifest -> files[section_base(scene)+id] (OGG in DATA3). Same resolution as set-texture.
-- **grounding:** source=frida, confidence=high
-- **evidence:** Frida capture: `play-bgm 0x5` in SC0000 (section base 0) loaded BGM006.OGG = files[5]. Unified with set-texture resolution rule.
+- **summary:** Play background music by id. BGM is addressed by DIRECT LITERAL NAME: id -> BGM{id:03d}.OGG (in DATA3), NOT the per-scene section manifest (that's voices/textures). E.g. play-bgm 5 -> BGM005.
+- **grounding:** source=investigation, confidence=high
+- **evidence:** By-ear confirmed (2026-07-06): SC0000 real game plays BGM005 for play-bgm 0x5 and BGM008 for play-bgm 0x8 (we initially mis-played BGM006/BGM009 via the manifest = off-by-one). Direct-name proven by play-bgm 0x23 -> BGM035.OGG, a real standalone track (BGM set skips 030-034) that the manifest mis-resolved to a graphics entry (EV049AA.AGF). CORRECTS the earlier 'unified manifest / Frida BGM006' claim, which was wrong by one. Voices/textures still use the manifest (files[base+id], offset 0). Diagnostic: `Age.Cli audio SC0000.BIN`.
 
 ### 0xc4 `play-voice` (play-voice, argc 1)
-- **summary:** Play a voice clip by id; id resolves via the SYS4INI section manifest -> files[section_base(scene)+id] (voice OGG in DATA1/DATA4). Same rule as set-texture/play-bgm.
-- **grounding:** source=investigation, confidence=med
-- **evidence:** Section-manifest resolution validated across archives incl. DATA4 voice OGGs (586/595 captured loads); per-clip id->OGG not individually Frida-pinned yet.
+- **summary:** Play a voice clip by id; id resolves via the SYS4INI section manifest -> files[section_base(scene)+id] (voice OGG in DATA1/DATA4). Same rule as set-texture (NOT play-bgm, which is direct-name BGM{id:03d}).
+- **grounding:** source=investigation, confidence=high
+- **evidence:** By-ear confirmed (2026-07-06): SC0000 prologue voices play on their lines via Godot AudioStreamPlayer. Off-by-one disproven structurally: manifest interleaves graphics/voice (files[35]=EV049AA, [36]=MAN999, [37]=EV052CA, [38]=SYL0001), so files[base+id] lands voices on OGGs while files[base+id-1] would land them on .AGF graphics (silent) -- and they play, so the offset is exactly 0. Lily's lines are correctly form-gated (G[0xa57/0xa58/0xa59]) and stay silent when no form flag is seeded -- not a bug.
 
 ## compute