feat(lint): wire Vale as commit-stage pre-commit hook

Adds vale-audit-prefilter as a local pre-commit hook scoped to skill/agent
markdown files, matching the invocation pattern skill-audit/agent-audit
already use. Runs at commit-stage only since it's a fast deterministic
prefilter; push-stage already covers the full test suite and manifest checks.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FxG5T8EJDgkABXxuneuFfn

.pre-commit-config.yaml

@@ -98,6 +98,15 @@ repos:
               fi
             done
 
+      - id: vale-audit-prefilter
+        stages: ['pre-commit']
+        name: Vale audit prefilter
+        description: Run Vale against skill/agent markdown files as a deterministic prefilter for skill-audit/agent-audit
+        entry: vale --config .vale.ini
+        language: unsupported
+        files: '^plugins/.*/(skills/.*/SKILL\.md|agents/.*\.md)$'
+        pass_filenames: true
+
   - repo: meta
     hooks:
       - id: check-hooks-apply