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

plugins/git/skills/pc-author/SKILL.md

@@ -66,7 +66,7 @@ Read `.pre-commit-config.yaml` first. Note any stale `rev` values (see **Rev sta
 1. Identify the hook entry and its repo block.
 2. State what will be removed: hook ID, and whether the parent repo block will also be deleted (if it would have zero hooks remaining). Wait for confirmation.
 3. Remove the hook entry. If the repo block now has zero hooks remaining, remove the entire repo block.
-4. Write. Run `pre-commit validate-config`. If non-zero: revert the edit, show the error, and stop — do not leave a broken config (removal edits are not safely auto-fixable, unlike a bad new hook block, which can usually be corrected in place).
+4. Write. Run `pre-commit validate-config`. If non-zero: revert the edit, show the error, and stop — do not leave a broken config (removal edits are not safely auto-fixable, unlike a bad new hook block, which can often be corrected in place).
 
 ### Configuring top-level keys