feat(linkedin-studio): S16 — optional manual saves in analytics + close deferred onboarding Write MAJOR

Lifts the original v4.0.0 Non-Goal: an optional, manually-entered `saves`
metric through the analytics layer, built location-agnostic (option c) so
UI-brief §9b/M0 relocates the data dir in one place later.

- types: PostMetrics.saves? + Weekly/Monthly summary.totalSaves? (optional);
  new RankableMetric type for the always-numeric index-access whitelist
- parser: dedicated parseOptionalCount() — blank/non-numeric/negative -> undefined
  ("unknown != 0"), genuine 0 kept; saves NOT folded into engagementRate
- reports: totalSaves set only when >=1 post carries saves (backward-compat)
- cli: saves surfaced in import summary + weekly/monthly totals + per-post
- S16-pre: onboarding.md allowed-tools gains Write (closes S15-deferred MAJOR)
- docs (three-doc rule): plugin README boundary + analytics README + root README
  + plugin CLAUDE.md + CHANGELOG; dwell stays explicitly unmeasurable

Independent /trekreview: brief-conformance 0 findings; code-correctness 2 MAJOR
(own lockstep misses) FIXED in-session (parseOptionalCount + edge tests). Gate:
tsc clean, analytics 116/116, lint 74/0/0, hooks 98/98. Within-v4.1.0 refinement
(no surface/count/version change).

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

README.md

@@ -120,7 +120,11 @@ Build authentic LinkedIn authority through algorithmic understanding, strategic
 
 - **Long-form newsletter pipeline** — a multi-phase orchestrator (research → skeleton → prose → de-AI/voice scrub → fact-check → editorial and persona gates → visual assets → lock → delivery) with maintained edition state
 - **Adversarial review** — cold headless content, language, and fact reviewers re-check a frozen draft with no drafting-session context; `/linkedin:pivot` re-opens cleared gates on major rewrites
-- **Content engine** — Content Matrix (40+ ideas from one topic), voice training with drift detection, full ideation → publish → 48-hour monitoring → analytics
+- **Content engine** — Content Matrix (40+ ideas from one topic), voice training with drift detection, full ideation → publish → 48-hour monitoring
+- **Honest analytics** — CSV-import pipeline with weekly/monthly reports and anomaly alerts. Adds an
+  **optional, manually-entered `saves`** count (add a `Saves` column with the number read off native
+  LinkedIn analytics; never auto-tracked, `unknown` ≠ 0, excluded from the engagement rate). `dwell`
+  time stays **explicitly unmeasurable** — no fabricated metric or surface
 - **Growth and monetization** — phase-specific guidance from 0 to 10K+ followers; topic-relevance profile optimization aligned to LinkedIn's 2026 ranking model
 
 Key commands: `/linkedin:create` + `/linkedin:measure` (journey front-doors), `/linkedin:onboarding`, `/linkedin:post`, `/linkedin:newsletter`, `/linkedin:report`