[norbot7865]

Summary

• adds deterministic linear parameter smoothing evaluated in the audio engine
• adds bounded authoritative automation lanes with exact start/end semantics
• implements linear, exponential, smoothstep, and hold curves
• implements explicit/current-start ramp, point-based automate, and immediate/scheduled cancellation
• deterministically replaces overlapping lanes and retains cancellation-frame values
• adds automation start/cancel scheduler events, trace output, high-water/cancellation statistics, and --automation-trace
• resets generation-specific automation safely on patch updates
• adds endpoint/formula, invalid curve/range/duration, smoothing, cancellation, overlap, nREPL ramp, and 64–1024 block invariance tests
• adds docs, fixture, make test-automation, and MP3 artifact

Validation

• make acceptance
• make test-automation
• go test -race ./internal/audio ./internal/lisp ./internal/nrepl
• linear fixture starts at frame 0 and completes exactly at frame 44100

Audio: examples/audio/issue-9-linear-automation.mp3

Closes #9.