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>

scripts/analytics/src/reports/weekly.ts

@@ -154,12 +154,23 @@ export function generateWeeklyReport(analyticsRoot: string, week?: string): Week
   }
 
   // Calculate summary metrics
+  let totalSaves = 0;
+  let sawSaves = false;
   for (const post of weekPosts) {
     report.summary.totalImpressions += post.metrics.impressions;
     report.summary.totalReactions += post.metrics.reactions;
     report.summary.totalComments += post.metrics.comments;
     report.summary.totalShares += post.metrics.shares;
     report.summary.totalClicks += post.metrics.clicks;
+    if (post.metrics.saves !== undefined) {
+      totalSaves += post.metrics.saves;
+      sawSaves = true;
+    }
+  }
+  // Only surface saves when at least one post carried it — keeps saves-free
+  // reports byte-identical to pre-saves output (backward-compat).
+  if (sawSaves) {
+    report.summary.totalSaves = totalSaves;
   }
 
   // Calculate averages