feat(lint): expand Vale audit prefilter into a broader plugin-content harness

Deferred item from PR #85 review. Per ADR-0013: cherry-picks two low-noise
rules from trialing write-good/alex against the real corpus (VagueQualifier,
SentenceOpenerThereIs) into styles/Kyberforge rather than adopting either
package wholesale (both are tuned for blog prose and were noisy on this
repo's terse, imperative instruction files - see the ADR's rejected-rule
list). Adds a new skill-size-check pre-commit hook enforcing agentskills.io's
500-line/5,000-token SKILL.md ceiling, currently unenforced. Fixes the 28
resulting violations across 20 existing SKILL.md/agent files so the
enforcing pre-commit hook lands clean.

governance.md/CONTROLS.md were evaluated and excluded as rule sources -
they're org/CI-infrastructure controls, not prose patterns Vale can express.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QUDczvw1H3eEeMD29Q9Lbi

.pre-commit-config.yaml

@@ -98,6 +98,15 @@ repos:
               fi
             done
 
+      - id: skill-size-check
+        stages: ['pre-commit']
+        name: SKILL.md size ceiling
+        description: Enforce agentskills.io's 500-line/5,000-token SKILL.md size ceiling
+        entry: scripts/skill-size-check.sh
+        language: script
+        files: '^plugins/[^/]+/skills/[^/]+/SKILL\.md$'
+        pass_filenames: true
+
       - id: vale-audit-prefilter
         stages: ['pre-commit']
         name: Vale audit prefilter