fix(viz): sakura + heartbeat AGC; remove firework

[vxcozy]

Summary

• sakura — route petal-spawn intensity through SpectrumScaler::normalise + stochastic fractional-carry so quiet volumes still precipitate.
• heartbeat — new sibling SampleScaler (sample-domain AGC, mirrors the SpectrumScaler attack/release philosophy) lifts the ECG trace off the baseline at typical listening volumes.
• firework — full deletion; visualiser catalogue drops 23 → 22. Module, enum variant, parse arms, carousel registration, pane_mode entry, fuzzy/command_bar test catalogues, README family list, and the cli.md reference row all removed.

Why

Live-testing v1.2.0 surfaced three viz bugs in the same class as CLI-89: amplitude-scaling math tuned for ≈1.0 signals silently fails at typical listening volumes (peak_sample ≈ 0.05–0.15).

Viz	Symptom	Root cause
sakura	black screen	spawn_count = (energy * 3.0) as usize truncates to 0 until energy ≥ 0.33
heartbeat	flat line	raw sample amplitudes map directly to Y-pixels, tiny samples = 1-pixel trace
firework	black screen	delta > TRANSIENT_THRESHOLD never trips at normal volume

The sakura and heartbeat fixes extend the CLI-89 pattern (PR #57): put the input on an envelope-follower AGC so typical listening volume reads as full-scale visual amplitude, with fast attack + slow release so transients pop and the gain ceiling doesn't strobe on brief dips.

SampleScaler is a bipolar-sample sibling to SpectrumScaler — SpectrumScaler does log/dB compression on magnitudes (non-negative), which doesn't cleanly map to [-1, 1] PCM samples; the sample-domain tracker keeps sign and tracks |sample| peak directly.

Firework's transient detector was the wrong reactive primitive for ambient audio — it required a sharp spike in already-smoothed energy, which essentially never occurs outside contrived test fixtures. Rather than re-tune (and introduce another ghost viz in the carousel), removed entirely.

Test plan

• cargo fmt --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace --all-features
• new unit tests:
  • scaling::sample_scaler_quiet_signal_fills_majority_of_range
  • scaling::sample_scaler_preserves_sign
  • scaling::sample_scaler_loud_transient_clamps_without_overshoot
  • scaling::sample_scaler_silence_does_not_auto_gain
  • scaling::sample_scaler_attack_faster_than_release
  • sakura::quiet_listening_volume_still_spawns_petals (≥10 petals over 30 frames at ~0.05 peak)
  • heartbeat::quiet_listening_volume_lifts_trace_off_baseline (≥20% of pane height)
  • heartbeat::loud_volume_saturates_without_overshoot (≥80% peak, clamped ≤1.0)
• manual: launch clitunes, press p to cycle to sakura, verify petals rain continuously at normal volume
• manual: cycle to heartbeat, verify the ECG trace sweeps across the pane instead of sitting flat on the baseline
• manual: :viz firework is rejected (name no longer in the catalogue)

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.