[ponytail#295] Extensible skill system — ponytail-review-uncommitted as sub-skill

[getappz]

Origin

DietrichGebert/ponytail#295

Problem

ponytail-review only works on committed diffs. Users want to review uncommitted changes before committing (pre-commit hook equivalent).

Rust port adaptation

Design the skill system to be extensible:

• Core review logic as a library function (takes diff input, returns findings)
• ponytail-review and ponytail-review-uncommitted are thin wrappers around the same core
• Skills should be composable — ponytail-review-uncommitted = git diff + ponytail-review
• Consider sub-skill registration system rather than hardcoded variants

Relevant files

• crates/ponytail/src/sub_skills.rs — sub-skill dispatch
• crates/ponytail/src/switcher.rs — detect(), SwitchAction

Acceptance

• Users can add new review variants without modifying core code
• ponytail-review-uncommitted works as a sub-skill
• Core review logic reused across all review variants

[getappz]

Progress update (not closing -- still partially open):

Skills are now user-extensible: crates/flare-code/src/sub_skills.rs's get_custom/custom_skill_names load arbitrary .md files from skills_dir() as new skill/mode variants without any core code changes — covers the acceptance criterion "users can add new review variants without modifying core code."

Still missing: a built-in review-uncommitted variant that reuses the core review logic against git diff (uncommitted changes) specifically — no such skill or git diff-sourced sub-skill exists yet.