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/SoundCookbook.cs

@@ -0,0 +1,83 @@
+using System;
+using System.Collections.Generic;
+using DatReaderWriter.DBObjs;
+using DRWSound = DatReaderWriter.Enums.Sound;
+
+namespace AcDream.Core.Audio;
+
+/// <summary>
+/// Probabilistic entry picker over a retail <see cref="SoundTable"/>.
+///
+/// <para>
+/// Each <see cref="DatReaderWriter.Enums.Sound"/> key in
+/// <c>SoundTable.Sounds</c> maps to a list of
+/// <see cref="DatReaderWriter.Types.SoundEntry"/> items each carrying a
+/// probability weight. Retail picks one entry per trigger by rolling the
+/// cumulative distribution — that's how footsteps sound slightly
+/// different each step, how weapon swings have 3 swoosh variants, etc.
+/// </para>
+///
+/// <para>
+/// r05 §4: the picker samples a uniform random in [0,1) and walks the
+/// entries accumulating probabilities; the first entry whose running total
+/// exceeds the sample wins. If all probabilities sum to &lt; 1, the
+/// remaining mass means "silence" — the call returns null. If probabilities
+/// sum to &gt; 1 the picker still works correctly (it clamps on the last
+/// entry).
+/// </para>
+/// </summary>
+public static class SoundCookbook
+{
+    /// <summary>
+    /// Pick one entry from a sound's variant list, weighted by probability.
+    /// Returns <c>null</c> when the rolled sample falls into the "silence"
+    /// remainder of the distribution (probability sum &lt; 1).
+    /// </summary>
+    public static DatReaderWriter.Types.SoundEntry? Roll(
+        IReadOnlyList<DatReaderWriter.Types.SoundEntry> entries,
+        Random rng)
+    {
+        ArgumentNullException.ThrowIfNull(entries);
+        ArgumentNullException.ThrowIfNull(rng);
+
+        if (entries.Count == 0) return null;
+        if (entries.Count == 1) return entries[0];
+
+        float sample = (float)rng.NextDouble();
+        float cum = 0f;
+        for (int i = 0; i < entries.Count; i++)
+        {
+            cum += Math.Max(0f, entries[i].Probability);
+            if (sample < cum) return entries[i];
+        }
+        // Fell past the last entry — either probabilities sum to >1 (return
+        // last) or < 1 and we rolled into the "silence" tail (return null).
+        float total = 0f;
+        for (int i = 0; i < entries.Count; i++)
+            total += Math.Max(0f, entries[i].Probability);
+
+        return total > 0.999f ? entries[entries.Count - 1] : null;
+    }
+
+    /// <summary>
+    /// Convenience lookup: given a SoundTable + a retail
+    /// <see cref="DRWSound"/> key (e.g. Swoosh1, Footstep1), roll the
+    /// entry list and return the winning entry. Returns null if:
+    /// <list type="bullet">
+    ///   <item><description><paramref name="table"/> has no mapping for
+    ///   <paramref name="sound"/>.</description></item>
+    ///   <item><description>The mapping's entry list is empty.</description></item>
+    ///   <item><description>The probability roll hits the silence
+    ///   tail.</description></item>
+    /// </list>
+    /// </summary>
+    public static DatReaderWriter.Types.SoundEntry? Roll(
+        SoundTable table,
+        DRWSound sound,
+        Random rng)
+    {
+        ArgumentNullException.ThrowIfNull(table);
+        if (!table.Sounds.TryGetValue(sound, out var soundData)) return null;
+        return Roll(soundData.Entries, rng);
+    }
+}