Changelog of @hackage/gb-synth 0.2.1.0

Changelog

Pulse waveform with variable duty cycle. Pulse !Double constructor on Waveform. Supports the four Game Boy duty cycles (0.125, 0.25, 0.5, 0.75). Square now delegates to Pulse 0.5 — fully backwards compatible.
Seventh chords. Four new Quality constructors: Dominant7, Major7, Minor7, Diminished7. All work with chord, inversion, and chordProgression.

Fix envelope discontinuity on fast notes. When note-on is shorter than attack+decay, the release now starts from the actual envelope level instead of jumping to the sustain level.
Fix duplicated envelope logic in Instrument: renderNote now delegates to Envelope.renderEnvelope instead of reimplementing the ADSR curve.
Fix hardcoded sample rate (22050) in Envelope — now uses sampleRate from WAV module.
Fix remaining Envelope field docs: adsrDecay and adsrRelease described as "exponential" but implementation is linear.

Update README: test count, GHC badge 9.6 → 9.8, Pulse and seventh chord API docs.

CI: add Haddock step before build (fixes stale .hi file coverage), upgrade GHC 9.6 → 9.8.
Tests: clean up temporary WAV files after roundtrip test.
182 pure tests (up from 161).

Fix Envelope module documentation (decay/release described as "exponential" but implementation is linear).
Add gb-vector as ecosystem companion in README.

Fix Haddock cross-references in Effects and Pattern modules.
Fix README chord progression descriptions and missing Pattern import.
Remove -O2 from library and test ghc-options (consumers set their own optimization).

GBSynth.SFX: 13 ready-to-use sound effect presets (laser, explosion, impact, alert, click, powerup, coin, jump, heal, defeat) plus pre-rendered drum samples (kickSample, snareSample, hihatSample). All built from synthesis primitives, no sample files.
GBSynth.Chord: Programmatic chord construction. Quality type (Major, Minor, Diminished, Augmented, Sus2, Sus4), chord / inversion / chordProgression builders, and built-in progressions (pop1564, blues145, minorClassic).
GBSynth.Effects: Post-processing effects — bitCrush, echo, fadeIn, fadeOut, reverseSignal, mix.

Eliminate partial functions: tail → drop 1 in Oscillator and Synthesis, maximum / foldl1 → safe foldl' with empty list guards in Render.

Initial release.

Oscillators: sine, square, saw, triangle, noise, pulse with configurable duty cycle
ADSR envelope generator with attack, decay, sustain, release stages
Instrument definition with oscillator type, envelope, and harmonics
Multi-channel pattern sequencer with note events and rests
Song structure: sections, tempo, time signature, instrument assignment