feat: honor canonical glide time for slide notes

[ChuxiJ]

Summary

• make slide-note playback honor positive canonical subtractive glideTime values instead of always overriding them with a fixed heuristic
• keep the existing heuristic as a fallback for zero-glide subtractive instruments, FM instruments, and legacy preset sources
• add focused node-environment tests for canonical override and fallback behavior

Why

Sprint 01 already exposes Glide Time in the synth editor and stores it in canonical track.instrument, but slide-note playback still ignored that value. This PR closes that runtime parity gap without changing the established feel for legacy/default slide playback.

Verification

• npx tsc --noEmit
• npx vitest run --environment node src/engine/__tests__/SynthEngine.test.ts
• npm run build

Notes

• This PR intentionally stays engine-only. It does not change the editor UI or store schema.

[ChuxiJ]

Triage: Hold — Stacked on synth improvement chain. Depends on #1019.

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