v0.3.0

Added

• Riff-locked drum generation: a new riff CLI subcommand and DrumGeneratorAPI.analyze_riff() analyze a recorded guitar/bass riff's rhythmic accents via onset detection (librosa) and lock a genre plugin's kick pattern onto them, while snare, hi-hat, cymbals, fills, and drummer styling still come from the normal generation pipeline untouched (#57). V1 scope: the riff is analyzed as one representative bar and tiled to fill --bars.
• RiffLockTransform modification, applied via PluginManager.apply_riff_lock() (routed through the plugins domain rather than generation importing modifications directly, per this project's existing DDD domain-boundary rules).
• Snare-accent-reaction: SnareAccentReaction reacts the snare to the same riff accents, in either reinforce mode (velocity-boosts existing snare hits near a strong accent) or stab mode (inserts a unison snare hit at very strong accents where riff-lock placed a kick but no snare was nearby, deterministically collapsing to reinforce instead of stacking a second hit when an existing snare is already close by). New --snare-mode/--snare-stab-threshold CLI flags and GenerationParameters.riff_snare_mode/riff_snare_stab_threshold fields; defaults to "off" (no behavior change unless explicitly enabled).
• New midi_drums.analysis package (a sibling of midi_drums.ai, not nested in it, so importing onset-detection code doesn't drag in the LangChain/pydantic-ai stack) and a new audio extras group (uv sync --group audio: librosa, soundfile, numpy).
• New REAPER create_beat_from_riff.lua action: select a riff item and run it to get a kick-locked drum pattern back. Uses the take's own audio source directly when available, or a bar-aligned time-selection render for MIDI/VSTi takes; corrects for riffs that don't start on a bar line via --offset-beats.

Fixed

• REAPER's io.popen command construction is now routed through cmd /S /C, avoiding a Windows quote-stripping bug that corrupted commands built from multiple quoted segments (surfaced as '...' is not recognized in AI-agent mode).
• CLI stdout/stderr are reconfigured to UTF-8 on Windows, avoiding a UnicodeEncodeError crash when AI-generated text containing non-ASCII characters is piped through REAPER's io.popen.
• GetUserInputs dialogs in create_song_sections.lua are now wide enough to comfortably read and edit free-text fields, especially the AI description prompt.
• The AI agent's system prompt now requires a complete song structure (6-8+ sections, including a chorus/hook and an outro) instead of allowing it to infer a bare 2-section song from a partial description.
• Release-notes generation (release.yml) no longer emits a spurious leading/trailing blank line around each version's changelog section.

No breaking changes - riff_snare_mode defaults to "off" (identical to pre-feature behavior) and every other addition is a new optional field/method/CLI flag; see docs/RELEASING.md for what counts as this project's public API surface.