feat(audio): Phase E.2 OpenAL engine + SoundTable cookbook + hook wiring

Full audio pipeline from MotionHook → OpenAL 3D playback. Faithful to
retail's 16-voice pool, inverse-square falloff, and SoundTable
probabilistic variant selection.

Core layer (AcDream.Core/Audio):
- WaveDecoder parses the WAVEFORMATEX in Wave dat headers. PCM
  (wFormatTag=1) decodes directly; MP3 (0x55) and ADPCM (0x02) return
  null + log (ACM compressed decoders need Windows winmm; cross-platform
  path deferred). Cites r05 §2.1-2.3 + ACE Wave.cs.
- SoundCookbook.Roll implements the probability-weighted entry pick that
  gives retail footsteps their variation. Cumulative-distribution walk;
  silence tail when probabilities sum to <1.
- DatSoundCache: ConcurrentDictionary-backed lazy load of Wave /
  SoundTable dats, decoded PCM memoized.

App layer (AcDream.App/Audio):
- OpenAlAudioEngine (Silk.NET.OpenAL): 16-source 3D pool with
  round-robin first-free, then evict-quieter-slot algorithm matching
  retail chunk_00550000.c FUN_00550ad0 exactly. Separate 4-source UI
  pool (source-relative). AL buffer cache keyed by Wave id.
  InverseDistanceClamped distance model. Fail-open when AL driver
  missing or ACDREAM_NO_AUDIO=1 — client continues without audio.
- AudioHookSink routes SoundHook / SoundTableHook / SoundTweakedHook
  from the Phase E.1 animation-hook router into OpenAL. All three
  hook types fire on both player AND NPCs/monsters (the sequencer
  dispatches per-entity and the sink uses entity worldPos for 3D pan).
- DictionaryEntitySoundTable holds per-entity SoundTable mapping,
  populated from Setup.DefaultSoundTable at hydration time. Server-
  sent overrides would take precedence here when wired.

GameWindow integration:
- OpenAL init in OnLoad after dat collection, suppressible via
  ACDREAM_NO_AUDIO=1.
- SetListener called each OnRender frame with camera position + view
  basis vectors (fwd = -Z, up = +Y of inverse view).
- AudioEngine disposed in OnClosing before dats.

Tests: 6 WaveDecoder (PCM / MP3-null / ADPCM-null / stereo / truncated
/ peek) + 6 SoundCookbook (empty / single / 50-30-20 distribution
within 5%, silence tail, table lookup, missing table key). Verified
against r05 §2 + ACViewer export-path.

Build green, 497 tests pass (up from 485).

Ref: r05 §2 (Wave format), §5.3 (16-voice pool + eviction).
Ref: FUN_00550ad0 (chunk_00550000.c:527) eviction algorithm.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Audio/DatSoundCache.cs

@@ -0,0 +1,78 @@
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using DatReaderWriter;
+using DatReaderWriter.DBObjs;
+
+namespace AcDream.Core.Audio;
+
+/// <summary>
+/// DatCollection-backed cache of decoded waves + SoundTable lookups.
+///
+/// <para>
+/// Lazy-loads each Wave / SoundTable on first request, decodes Wave PCM
+/// data via <see cref="WaveDecoder"/>, and memoizes the result. Safe to
+/// call from any thread — the inner dicts are
+/// <see cref="ConcurrentDictionary{TKey,TValue}"/>.
+/// </para>
+///
+/// <para>
+/// Returns <c>null</c> for waves whose format tag isn't PCM (MP3 / ADPCM
+/// fall through silently until a compressed-decoder path is wired up).
+/// </para>
+/// </summary>
+public sealed class DatSoundCache
+{
+    private readonly DatCollection _dats;
+    private readonly ConcurrentDictionary<uint, WaveData?> _waves = new();
+    private readonly ConcurrentDictionary<uint, SoundTable?> _tables = new();
+
+    public DatSoundCache(DatCollection dats)
+    {
+        _dats = dats;
+    }
+
+    /// <summary>
+    /// Retrieve decoded PCM data for a Wave dat id. Returns null if the
+    /// wave is missing, malformed, or uses a currently-unsupported format
+    /// (MP3 / ADPCM).
+    /// </summary>
+    public WaveData? GetWave(uint waveId)
+    {
+        if (_waves.TryGetValue(waveId, out var cached)) return cached;
+
+        var wave = _dats.Get<Wave>(waveId);
+        if (wave is null)
+        {
+            _waves[waveId] = null;
+            return null;
+        }
+
+        var decoded = WaveDecoder.Decode(wave.Header, wave.Data);
+        _waves[waveId] = decoded;
+        return decoded;
+    }
+
+    /// <summary>
+    /// Retrieve a SoundTable by dat id. Returns null if the table is
+    /// missing from the dats.
+    /// </summary>
+    public SoundTable? GetSoundTable(uint soundTableId)
+    {
+        if (_tables.TryGetValue(soundTableId, out var cached)) return cached;
+
+        var table = _dats.Get<SoundTable>(soundTableId);
+        _tables[soundTableId] = table;
+        return table;
+    }
+
+    /// <summary>
+    /// Total number of waves that have been accessed (hit or miss).
+    /// Useful for diagnostic overlays.
+    /// </summary>
+    public int CachedWaveCount => _waves.Count;
+
+    /// <summary>
+    /// Total number of SoundTables that have been accessed.
+    /// </summary>
+    public int CachedSoundTableCount => _tables.Count;
+}