feat(animation): chromatic_aberration, a red/cyan fringe on any node

[LeadcodeDev]

Refs #344 — its point 4.

chromatic_wipe splits the red and cyan channels, but only as a scene transition. A reference video shows an icon card arriving with channel separation — a per-element effect.

{ "style": { "animation": [{ "name": "chromatic_aberration", "amount": 6, "duration": 0.6 }] } }

amount (px, default 6) is the peak separation, reached at delay, decaying via easing (default ease_out) to exactly 0 by delay + duration — verified pixel-identical to no effect at all at that point, so no node is left permanently fringed.

How it is drawn

It builds a single Skia ImageFilter: the node's own layer, shifted and colour-matrixed to isolate red one way and cyan the other, summed with BlendMode::Plus. That filter is composed with any existing style.filter and fed into the same save_layer that already handles opacity and filters — so it inherits that layer's bleed-bounds logic (extended by the current shift) for free. No new layer, no manual pixel buffers.

active_chromatic_aberration mirrors active_shimmer's existing read-off-css.animation pattern.

A deliberate departure from chromatic_wipe

The isolated channels are paired as {R} vs {G+B}, not chromatic_wipe's {R} vs {B}. A naive red-vs-blue split gives red and yellow edges; pairing green with blue gives red and cyan, which is what the issue's own wording asks for. Left edge reads pure red, right edge pure cyan.

The curve differs too, and on purpose: chromatic_wipe is a symmetric tent, zero at both ends, because a transition must not leave a fringe bleeding into the next scene. This is an arrival — maximum at the start, zero at the end.

Two edits outside the brief, both forced

Flagging these rather than burying them:

• schema/video.rs — AnimationEffect, the #[serde(tag = "name")] enum every style.animation entry parses through, lives here and not in schema/animation.rs. The JSON in the issue cannot deserialize without a variant here. One import, one variant, one shift_delay arm, same shape as the neighbouring Shimmer/Glow.
• cli/commands/validate_schema.rs — the new variant made entrance_budget's exhaustive match an E0004. The fix is not merely a compile fix, it is the right semantic: a scene shorter than delay + duration now errors with "animation finishes at 0.60s ... but scene_duration is 0.30s — it will be truncated", which extends the "nothing left fringed" guarantee to validation time. Verified with a real rustmotion validate run.

Verification

9 tests: 3 serde (including deny_unknown_fields and the exact JSON from the issue), 3 on the shift curve, 3 pixel-level in paint_order_tests.

Proven to catch the absence — forcing the filter to None:

chromatic_aberration_shows_a_red_fringe_on_one_edge_and_a_cyan_fringe_on_the_other
panicked: expected a red-leaning fringe on the left edge mid-flight,
got (255, 255, 255)

cargo fmt --all --check, cargo clippy --workspace --all-targets -- -D warnings, cargo test --workspace (1534) all clean.

Written comment-free, per the codebase-wide rule from #345.