feat: professional reggaeton production engine — 7 SDD changes, 302 tests

- section-energy: track activity matrix + volume/velocity multipliers per section
- smart-chords: ChordEngine with voice leading, inversions, 4 emotion modes
- hook-melody: melody engine with hook/stabs/smooth styles, call-and-response
- mix-calibration: Calibrator module (LUFS volumes, HPF/LPF, stereo, sends, master)
- transitions-fx: FX track with risers/impacts/sweeps at section boundaries
- sidechain: MIDI CC11 bass ducking on kick hits via DrumLoopAnalyzer
- presets-pack: role-aware plugin presets (Serum/Decapitator/Omnisphere per role)

Full SDD pipeline (propose→spec→design→tasks→apply→verify) for all 7 changes.
302/302 tests passing.

AGENTS.md

@@ -0,0 +1,22 @@
+# Code Review Rules
+
+## Python
+- Type hints on all function signatures
+- Dataclasses over dicts for structured data
+- Deterministic output: seed-based RNG, no global random state
+- No bare except clauses
+
+## Architecture
+- Separate modules by concern (calibrator, composer, builder, selector, validator)
+- Post-processing over inline modification (Calibrator.apply() pattern)
+- Schema changes must be backward-compatible (new fields get defaults)
+
+## Testing
+- pytest only
+- Unit tests for all new functions
+- Integration tests for end-to-end flows
+- Regression: existing tests must not break
+
+## SDD
+- All changes follow SDD pipeline: propose → spec → design → tasks → apply → verify
+- Artifacts stored in .sdd/changes/<change-name>/