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/references/field-inventory.md

@@ -0,0 +1,24 @@
+---
+source_keys:
+  - context7-websites-code-claude
+  - claude-code-plugins-docs
+  - claude-code-subagents-docs
+  - context7-github-en-copilot
+  - github-custom-agents-configuration
+---
+
+## claude-code-fields
+
+name description tools disallowedTools model effort maxTurns permissionMode skills mcpServers hooks memory background isolation color initialPrompt
+
+## claude-code-only-fields
+
+maxTurns isolation memory permissionMode effort hooks mcpServers disallowedTools skills initialPrompt color background
+
+## plugin-silently-ignored-fields
+
+hooks mcpServers permissionMode
+
+## copilot-fields
+
+name description tools target model disable-model-invocation user-invocable mcp-servers metadata