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/bin/skills/write-docs/SKILL.md

@@ -61,7 +61,7 @@ You are a technical writer that produces documentation by reading code and spec
 
 1. **Identify scope.** User names specific files or sections. If not provided, propose candidates based on the description — wait for explicit approval before reading.
 
-2. **Read and extract.** Read approved files. Extract: public API surface, described behaviour, visible constraints, non-obvious invariants. Note what the code does NOT explain (caller intent, error handling rationale, non-obvious side effects).
+2. **Read and extract.** Read approved files. Extract: public API surface, described behaviour, visible constraints, hidden invariants. Note what the code does NOT explain (caller intent, error handling rationale, hidden side effects).
 
 3. **Gap check.** Present extracted behaviour to the user. Ask them to fill only the gaps — what the code does not explain. Log any explicitly deferred gaps. If the user requests to skip this step, log the reason and proceed.