fix(viz): render braille visualisers edge-to-edge

[vxcozy]

Summary

• Pulse grows its pulsing disc against the longer half-axis so it fills the pane on wide terminals instead of hugging the middle with black gutters.
• Scope is intrinsically square in signal space (Lissajous XY) so it letterboxes with a muted phosphor-green gutter rather than stretching.
• Wave, Heartbeat, BarsDot now paint empty cells with their palette's muted backdrop colour instead of raw black.
• Every touched visualiser gains a 120x40 render test asserting that each edge row and column carries either painted dots or palette-tinted cells.

Why

Slice 1 (#54) removed the outer 1-col / 2-row pane inset so the cell grid stretches to the full pane. This slice fixes the remaining within-grid emptiness: braille visualisers that painted small centred shapes with large pure-black gutters around them. The pane now reads as "the viz chose this shape" rather than "the viz is broken" across the whole braille family.

The rewrite temptation for Scope was resisted — its Lissajous curve is inherently square, so it letterboxes with a muted phosphor tint instead of being stretched into an oval. Other geometrically-uniform viz (metaballs, terrain, retro, sakura, firework, scatter, butterfly, rain, binary, moire, tunnel, vortex, plasma, ripples, fire, matrix, bars_outline, classic_peak, density_ramp) already cover the full pane and were left untouched.

Test plan

• cargo fmt --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace --all-features
• new unit tests: pulse::fills_pane_at_120x40, wave::gutter_is_tinted_not_black, heartbeat::gutter_is_tinted_not_black, scope::letterboxed_gutter_is_tinted, bars_dot::gutter_is_tinted_not_black
• manual: launch clitunes in tmux pane, verify each touched viz fills the pane

[chatgpt-codex-connector]

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