Initial release: 8-bit sound synthesizer with LLM/MCP integration

Soundgen is a Rust workspace for generating 8-bit/chiptune sound effects,
UI sounds, and ambient textures for game audio assets. It features JSON-first
sound specs, an MCP server for LLM tool-use, an egui GUI editor, and a
runtime library with NES-authentic DAC emulation.

Features:
- 6 voice types: pulse, triangle, noise, DPCM, wavetable, FM
- Effects: ADSR envelope, frequency sweep, biquad filter, vibrato
- 13 built-in presets (SFX/UI/ambient) as JSON data files
- MCP server: list_presets, generate_sfx, render_sound tools
- Pattern-based sequencer (JSON song format)
- egui GUI: virtual keyboard, preset browser, channel editor, undo/redo
- Runtime: NES nonlinear DAC + SoundBank for game embedding
- 90 tests, 0 warnings

Crates:
- soundgen-core: synthesis engine (no I/O)
- soundgen-fmt: SoundSpec JSON schema + PresetRegistry
- soundgen-io: WAV writer + audio playback
- soundgen-seq: sequencer (patterns, songs)
- soundgen-cli: gen/render/render-song/list-presets
- soundgen-mcp: MCP server for LLM integration
- soundgen-gui: egui editor
- soundgen-runtime: NES DAC + SoundBank

presets/sfx/explosion.json

@@ -0,0 +1,35 @@
+{
+  "name": "explosion",
+  "duration": 0.8,
+  "sample_rate": 44100,
+  "channels": [
+    {
+      "type": "noise",
+      "mode": "white",
+      "frequency": 12000,
+      "filter": {
+        "type": "lowpass",
+        "cutoff": 3000,
+        "cutoff_sweep": { "start": 3000, "end": 100, "curve": "exponential" },
+        "q": 0.7
+      },
+      "envelope": { "attack": 0.002, "decay": 0.6, "sustain": 0.0, "release": 0.18 },
+      "volume": 0.85,
+      "pan": 0.0
+    },
+    {
+      "type": "noise",
+      "mode": "white",
+      "frequency": 4000,
+      "filter": {
+        "type": "lowpass",
+        "cutoff": 800,
+        "cutoff_sweep": { "start": 800, "end": 50, "curve": "exponential" },
+        "q": 1.0
+      },
+      "envelope": { "attack": 0.0, "decay": 0.4, "sustain": 0.0, "release": 0.1 },
+      "volume": 0.5,
+      "pan": 0.0
+    }
+  ]
+}