Add rich styling, box layout, and CSS-inspired gradient support

[Copilot]

• Review new feedback about named colors and config schema generation
• Inspect current config schema generation, config types, and named-color parsing
• Switch named-color parsing to cssparser-color
• Replace config.schema.toml with schemars-generated JSON schema in the config directory
• Update docs and any generation/build hooks for the new schema flow
• Run targeted tests, then full fmt/clippy/build/test validation
• Reply to the new PR feedback with the addressing commit hash

[MuntasirSZN]

@copilot This is good yet fragile. We are doing manual parsing. Use cssparser or a true parser to handle this. (Less fragile). Also drop colored, use anstyle. (Much more higher level, owo-colors if even higher).

[MuntasirSZN]

Use cssparser-color for named colors @copilot

Also drop config.schema.toml. use schemars to generate json schema in config dir (and add docs so user uses that) (taplo and tombi).

[Copilot]

@copilot This is good yet fragile. We are doing manual parsing. Use cssparser or a true parser to handle this. (Less fragile). Also drop colored, use anstyle. (Much more higher level, owo-colors if ev...

Addressed in c8f6899. Gradient/color parsing now goes through cssparser token parsing instead of manual string parsing, and terminal styling was switched from colored to anstyle while preserving the existing output behavior.