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/ui/error.json

@@ -0,0 +1,15 @@
+{
+  "name": "error",
+  "duration": 0.2,
+  "sample_rate": 44100,
+  "channels": [
+    {
+      "type": "pulse",
+      "duty": 50,
+      "frequency": { "start": 200, "end": 150 },
+      "envelope": { "attack": 0.005, "decay": 0.05, "sustain": 0.3, "release": 0.12 },
+      "volume": 0.4,
+      "pan": 0.0
+    }
+  ]
+}