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/presets-pack/proposal.md

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+# Proposal: presets-pack
+
+## Intent
+
+All plugins use the SAME flat preset regardless of track role (bass/lead/chords/pad) or genre context. A Serum_2 on a bass track gets the same sound as Serum_2 on a lead track. Professional reggaeton needs role-specific timbres: deep sine 808 for bass, detuned saw for lead, warm pad for chords, evolving texture for pad. Same for FX: Decapitator on drums needs aggressive drive, on bass needs subtle warmth.
+
+## Scope
+
+### In Scope
+- Restructure `PLUGIN_PRESETS` from flat `{plugin: [chunks]}` to role-aware `{plugin: {role: [chunks]}}`
+- Create role-specific presets for plugins used in multiple roles: **Serum_2** (bass/lead), **Omnisphere** (chords/pad), **Decapitator** (drums/bass)
+- Programmatically derive new presets by base64-decoding existing presets (Serum=JSON, SoundToys=key=value), modifying genre-specific parameters, re-encoding
+- Update `make_plugin()` in `compose.py` and `_build_plugin()` in `__init__.py` to resolve role-aware presets
+- Add fallback: if no role-specific preset exists, use existing default preset
+
+### Out of Scope
+- Creating presets from scratch in REAPER (requires GUI — can't programmatically)
+- ReaScript-based preset capture (Phase 2)
+- Presets for all 113 plugins — only multi-role targets initially
+- Pro-Q 3 reggaeton EQ curve (no decodable format available)
+
+## Capabilities
+
+### New Capabilities
+- `presets-pack`: Role-specific plugin preset resolution and preset data management
+
+### Modified Capabilities
+None — existing plugin resolution unchanged; backward-compatible fallback to default preset.
+
+## Approach
+
+**Option B — Programmatic modification of decodable presets:**
+
+1. **Serum_2**: Decode base64 → JSON. Serum preset JSON has `component: "processor"` block with oscillator/wavetable/filter data. Create variants by modifying oscillator type (sine for bass, saw for lead), filter cutoff, envelope settings. Re-encode.
+
+2. **Decapitator (SoundToys)**: Decode base64 → key=value text (`WIDGET = Decapitator;...`). Create "aggressive" (high Drive, Tone bright) for drums, "warm" (low Drive, Tone dark) for bass. Re-encode.
+
+3. **Omnisphere**: Decode base64 → `SynthMaster` text block. Create "warm pad" variant with slow attack, filter modulation; "evolving texture" with movement/LFO. Re-encode.
+
+No GUI or REAPER needed — pure Python string processing over decoded preset text.
+
+## Affected Areas
+
+| Area | Impact | Description |
+|------|--------|-------------|
+| `src/reaper_builder/__init__.py` | Modified | `PLUGIN_PRESETS` restructured; `_build_plugin()` accepts role param |
+| `src/composer/templates.py` | Modified | `_parse_vst_block()`, `make_plugin()` resolution updated |
+| `scripts/compose.py` | Modified | `make_plugin()` passes role; `FX_CHAINS` keys used for role |
+| `src/core/schema.py` | Unchanged | `PluginDef` already has `preset_data` field |
+
+## Risks
+
+| Risk | Likelihood | Mitigation |
+|------|------------|------------|
+| Modified preset crashes plugin on load | Low | Each variant derived from working ground-truth preset; only tweak known-safe params |
+| Base64 decode/re-encode breaks binary integrity | Low | Round-trip test per plugin: decode → encode → bytes equal |
+| Omnisphere text format undocumented | Med | Preserve structure, only modify known `ATTRIBUTE` values visible in decoded text |
+
+## Rollback Plan
+
+Revert `PLUGIN_PRESETS` to flat dict. Remove role param from `_build_plugin()` and `make_plugin()`. Existing tests verify preset injection still works.
+
+## Dependencies
+
+- `data/sample_index.json` (independent — not affected)
+- Existing ground-truth presets in `PLUGIN_PRESETS` (source material for variants)
+
+## Success Criteria
+
+- [ ] `python scripts/compose.py --bpm 99 --key Am` produces .rpp where Serum_2 on bass track has different preset data than Serum_2 on lead track
+- [ ] 110 existing tests continue to pass (backward-compatible fallback)
+- [ ] Round-trip test: decode → modify → encode produces valid base64 matching original length structure
+- [ ] At least 3 (plugin, role) combinations have distinct preset variants