chore(skills): rename all skills to domain-action convention

Adopts the whatsinagame naming pattern where the domain comes
first and the action second (e.g. pr-review, sprint-start,
audio-gen). Updated all cross-references in settings, agents,
docs, and inter-skill references.

12 renames: commit→git-commit, create-skill→skill-create,
gen-audio→audio-gen, gen-image→image-gen, plan-sprint→sprint-plan,
push-pr→pr-push, render-sprite→sprite-gen, review-pr→pr-review,
search-docs→docs-search, start-sprint→sprint-start,
start-workshop→workshop-start.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/workshops/test-architecture/justine-round2.md

@@ -274,7 +274,7 @@ Safe to create PR.
 - Does not run Layer 3 subprocess tests (too slow, nightly-tier)
 - Does not run performance benchmarks (machine-dependent, separate target)
 - Does not run Gauntlet golden file tests (depends on Gauntlet implementation)
-- Does not push or create the PR (that's `make push-pr` or the `/push-pr` skill)
+- Does not push or create the PR (that's `make pr-push` or the `/pr-push` skill)
 
 These are separate targets for developers who want deeper verification: