fix(linkedin-studio): close v4.0.0 audit review findings (S8)

Close the 5 findings from the S7 /trekreview release gate (review.md, verdict BLOCK):

- BLOCKER: comment-multiplier "5x" reconciled to the canonical order-only framing
  (no fixed multiplier) in agents/engagement-coach.md, linkedin-growth-playbook,
  linkedin-formats.md — per algorithm-signals-reference.md ("do not quote a comment
  multiplier").
- BLOCKER: carousel rate "6.60%/6.6% (highest)" reconciled to "~7% top organic
  format" in linkedin-formats.md:42 (was self-contradicting :50) and
  assets/templates/carousel-templates.md.
- Lint hardening: test-runner.sh STALE_STATS now matches 6.60% + the 5x comment
  folklore and scans agents/ + assets/templates/ — the grep that defines the
  Phase-0 criterion now catches both BLOCKERs.
- MAJOR: onboarding.md command count 26 -> 27.
- MAJOR: add section-append-branch (production-path) tests for recordFirstHourPlan
  + recordOutreachContact against a template-layout fixture.
- MINOR: move date-scalar changes.push inside the write branch in state-updater.mjs.

Verify: node --test hooks/scripts/__tests__/*.test.mjs -> 92/92; bash
scripts/test-runner.sh -> 66/0/0. NO push until /trekreview re-confirms ALLOW/WARN.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugins/linkedin-studio/references/linkedin-growth-playbook-2025-2026.md

@@ -42,7 +42,7 @@ Complete reference guide for growing from hundreds to thousands of engaged follo
 
 **Comment Value:**
 - Comments rank above likes in the engagement order (saves > shares > quality comments > reactions; see `references/algorithm-signals-reference.md`)
-- Comments: **5x more effective** than reshares
+- Comments: high-value engagement signal, but ranked below saves and shares — no verified fixed multiplier
 - Comments over 15 words: **2x impact** vs shorter ones
 - Comments from relevant professionals: Significantly higher weight than generic responses