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.

.sdd/changes/smart-chords/spec.md

@@ -0,0 +1,47 @@
+# Chords Specification
+
+## Purpose
+
+Chord progression generation with voice leading, inversion selection, and emotion-aware patterns for reggaeton. Deterministic and testable.
+
+## Requirements
+
+| # | Requirement | Strength | Key Scenarios |
+|---|------------|----------|---------------|
+| R1 | `ChordEngine(key, seed)` MUST produce identical progressions for same seed+key | MUST | Same seed → same notes; different seed → different notes |
+| R2 | Voice leading MUST minimize semitone movement between consecutive chords, capping at 4 semitones per voice | MUST | 2-chord transition ≤4 semitones per voice; 8-bar progression all leaps ≤4 |
+| R3 | SHALL support 3 inversion modes: `root`, `first`, `second` | SHALL | Root: lowest note = root; First: lowest = third; Second: lowest = fifth |
+| R4 | MUST support 4 emotion modes: `romantic`, `dark`, `club`, `classic` | MUST | Each emotion yields distinct degree sequence; unknown emotion → `classic` fallback |
+| R5 | `progression(bars, emotion, beats_per_chord, inversion)` SHALL return `list[list[int]]` — ordered chord voicings as MIDI note lists | SHALL | 8 bars @ 4 BpC → 8 chords; empty list for 0 bars |
+| R6 | Reggaeton progressions SHOULD use genre-appropriate cadences per emotion | SHOULD | Romantic: i-VI-III-VII; Dark: i-iv-V-v; Club: i-VII-VI-V; Classic: i-VI-III-VII |
+| R7 | `build_chords_track()` SHALL delegate to `ChordEngine` instead of hardcoded progression | SHALL | CLI `--emotion dark` → dark progression in output |
+
+### Scenario: Deterministic reproducibility
+
+- GIVEN `ChordEngine("Am", seed=42)`
+- WHEN `progression(bars=8)` called twice
+- THEN both calls return identical `list[list[int]]`
+
+### Scenario: Voice leading within bounds
+
+- GIVEN any 2 consecutive chords from a progression
+- WHEN computing voice leading
+- THEN no voice moves more than 4 semitones from its previous position
+
+### Scenario: Emotion modes diverge
+
+- GIVEN `ChordEngine("Am", seed=0)` with emotions `romantic`, `dark`, `club`, `classic`
+- WHEN `progression(8)` called per emotion
+- THEN all 4 output sequences differ
+
+### Scenario: Invalid emotion falls back
+
+- GIVEN `ChordEngine("Am")` with emotion `"angry"` (unknown)
+- WHEN `progression(8)` called
+- THEN defaults to `classic` progression, no error raised
+
+### Scenario: Integration with compose.py
+
+- GIVEN `python scripts/compose.py --key Am --emotion dark --output test.rpp`
+- WHEN build completes
+- THEN Chords track contains voicings matching dark-emotion progression