[wieslawsoltes]

Problem

WebScene exposed animation-direction in CSS metadata but discarded it during parsing and sampling, so supported keyframes always ran forward.

Result

• Parses and retains longhand/CSSOM and the first-animation shorthand values normal, reverse, alternate, and alternate-reverse.
• Adds a bounded direction enum to animation configuration and signatures.
• Maps cycle parity/progress before opacity, rotation, and filter sampling.
• Handles negative delays, infinite cycles, exact iteration edges, finite integer/fractional terminal points, and direction-correct existing forwards/both fill.
• Preserves exact filter-none stops, reduced motion, visibility, detach, frame-demand, lifecycle, and one-animation bounds.
• Adds deterministic native cases, a bounded WPT-aligned browser contract/profile, capability metadata, and validation documentation.
• Adds no ABI or AppScene change.

Play-state, backwards fill, multiple animations, WAAPI, and additional animated properties remain deferred under #242.

Closes #659.

Validation

git diff --check passed. Under the agreed fast merge policy, no local builds or runtime tests were run.