feat(kyberforge): add pc-author and pc-run pre-commit skills

## Why
Pre-commit config management was entirely manual — no skill existed to
help create, modify, or validate `.pre-commit-config.yaml`, or to run,
install, and maintain the pre-commit setup. These two skills close that
gap with clear scope separation: authoring vs. execution.

## Implementation Notes
- `pc-author` owns `.pre-commit-config.yaml` only (no hook publishing,
  no install). Runs `pre-commit validate-config` after every write.
  Shallow file-extension scan drives proactive hook recommendations;
  rev staleness is flagged against `references/hooks-by-language.md`
  rather than hardcoded versions. Remove path reverts on failure.
- `pc-run` owns install, run, autoupdate, gc, and clean. Defaults to
  `--all-files`. Install warns about existing `.git/hooks/` files being
  overwritten by `-f`. Clean requires HITL confirmation. Failure
  interpretation delegates to `references/failure-patterns.md`.
- Provenance wired to `plugins/kyberforge/docs/research/docs/pre-commit/`.
- Both skills resolve via the existing `"skills/"` glob in `plugin.json`.

## Impact
Two new slash commands available after `claude plugin install kyberforge@holocron`:
`/pc-author` and `/pc-run`.

Refs: #12

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01P87CiC58Ru2PPWYTeXtjHT

plugins/kyberforge/skills/pc-run/references/README.md

@@ -0,0 +1,6 @@
+# references/
+
+| File | Purpose |
+|---|---|
+| `failure-patterns.md` | Hook failure causes and concrete fix suggestions — loaded when hooks fail |
+| `sources.md` | Provenance: research sources that informed this skill |