feat(kyberforge): add agent-audit skill (closes #11)

## Why

agent-author produces paired agent definition files (Claude Code .md +
Copilot .agent.md) but had no companion audit skill to validate them.
agent-audit fills that gap, giving the same structured PASS/FAIL report
that skill-audit provides for SKILL.md files.

## Implementation Notes

- validate.sh uses scope detection (walk up for plugin.json / .git) to
  locate the counterpart file and determine whether plugin-silently-ignored
  fields (hooks, mcpServers, permissionMode) should be flagged
- CC-only and silently-ignored field lists are read from
  references/field-inventory.md at runtime rather than hardcoded —
  provenance back to the research corpus; see ADR-0019
- Single-file invocation (pass either file, counterpart derived) chosen
  over directory or name+root — see ADR-0018
- 12 bats tests cover provider detection, scope detection, all FAIL paths,
  and clean-pair pass

## Impact

- kyberforge bumped to v1.1.2
- agent-author close step should be updated to reference agent-audit (#11)
- Provenance/sources chain check deferred to #60

ADR: docs/adr/0018-agent-audit-single-file-invocation.md
ADR: docs/adr/0019-agent-audit-field-inventory-reference.md
Refs: #11
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0147vXtL5sP6vorDdqXGJJU9

plugins/kyberforge/skills/agent-audit/README.md

@@ -0,0 +1,28 @@
+# agent-audit
+
+Audits a Claude Code and Copilot agent definition file pair for correctness and quality.
+
+## What it does
+
+Accepts either file in a CC `.md` / Copilot `.agent.md` pair, derives the counterpart automatically, and validates both. Runs structural checks via `validate.sh` (required fields, kebab-case name, no placeholders, no CC-only fields in the Copilot file, silently-ignored fields at plugin scope), then qualitative checks on description phrasing and system prompt quality. Produces a compact findings report in the same format as `skill-audit`.
+
+## Usage
+
+```
+/agent-audit
+```
+
+Pass the path to either agent file as the argument.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | Skill instructions for agents |
+| `references/README.md` | Directory documentation for references/ |
+| `references/field-inventory.md` | Authoritative list of valid CC and Copilot agent fields |
+| `references/sources.md` | Research provenance for skill content |
+| `scripts/README.md` | Directory documentation for scripts/ |
+| `scripts/validate.sh` | Structural validation script for agent file pairs |
+| `tests/README.md` | Bats test dependency and run instructions |
+| `tests/validate.bats` | Bats tests for validate.sh |