test(contracts): Phase 0.a contract snapshots for audio surface

Snapshot the three public surfaces the audio-engine decomposition must not
change (docs/audio-engine-tlc.md Part IV §4): addon export table, audio-bridge
IPC channels, preload audio/audioEffects API keys. contract-check.test.js
diffs regenerated surfaces against the committed snapshots.

result-shapes.json (golden result key/type shapes) is deferred until the
engine_units harness can run the addon against a null device.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/contracts/addon-exports.json

@@ -0,0 +1,103 @@
+[
+  "addSource",
+  "bindInputDevice",
+  "clearChain",
+  "clearStreamOutput",
+  "closePluginEditor",
+  "detectNotes",
+  "enableFileLogging",
+  "getBackingDuration",
+  "getBackingLevel",
+  "getBackingPosition",
+  "getBufferSizes",
+  "getChainState",
+  "getCurrentDevice",
+  "getDeviceMetrics",
+  "getDeviceTypes",
+  "getKnownPlugins",
+  "getLevels",
+  "getNoteVerdicts",
+  "getParameters",
+  "getPitchDetection",
+  "getRawAudioFrame",
+  "getRawPitchDetection",
+  "getRendererBusMetrics",
+  "getSampleRate",
+  "getSampleRates",
+  "getSourceLevels",
+  "getSourceNoteVerdicts",
+  "getSourcePitchDetection",
+  "getSourceRawAudioFrame",
+  "getSourceRawPitchDetection",
+  "getStreamOverflowCount",
+  "getStreamSinkLevel",
+  "getStreamUnderflowCount",
+  "init",
+  "isAudioRunning",
+  "isBackingPlaying",
+  "isMlNoteDetection",
+  "isMonitorMuted",
+  "isStreamOutputActive",
+  "listInputDevices",
+  "listSources",
+  "loadBackingTrack",
+  "loadIR",
+  "loadNAMModel",
+  "loadNoteModel",
+  "loadPluginList",
+  "loadPreset",
+  "loadVST",
+  "moveProcessor",
+  "openPluginEditor",
+  "probeDeviceOptions",
+  "pushRendererAudio",
+  "removeProcessor",
+  "removeSource",
+  "replaceIR",
+  "resetPeaks",
+  "savePluginList",
+  "savePreset",
+  "scanPlugins",
+  "scoreChord",
+  "scoreSourceChord",
+  "seekBacking",
+  "sendMidiToSlot",
+  "setBackingSpeed",
+  "setBranch",
+  "setBranchSrc",
+  "setBypass",
+  "setChart",
+  "setCrashedPlugins",
+  "setDevice",
+  "setDeviceType",
+  "setGain",
+  "setInputChannel",
+  "setInputDeviceType",
+  "setMonitorKill",
+  "setMonitorMute",
+  "setMonitorMuteSuppressed",
+  "setMultiBypass",
+  "setNoiseGate",
+  "setNoteDetectionEnabled",
+  "setOutputDeviceType",
+  "setPan",
+  "setParameter",
+  "setPostGain",
+  "setRendererBus",
+  "setSlotState",
+  "setSourceChart",
+  "setSourceInputChannel",
+  "setSourceMonitorMute",
+  "setSourceVerifierOffset",
+  "setStreamBus",
+  "setStreamBusGain",
+  "setStreamOutputDevice",
+  "setTonePolish",
+  "setVstCrashSentinelPath",
+  "shutdown",
+  "startAudio",
+  "startBacking",
+  "stopAudio",
+  "stopBacking",
+  "unbindInputDevice"
+]