feat(project-bootstrap): v1.3.0 — idempotent CLAUDE.md merge on upgrade

Step 5 was binary on upgrade (append whole template / leave alone), so
projects bootstrapped before v1.2.0 silently missed new canonical triggers
(`check across all projects`, `we're on Windows`) on re-run. Now upgrade
reads existing CLAUDE.md, substring-diffs vs template, preserves a
deliberately-pinned platform line, and appends only missing lines after
explicit confirm. Re-runs are no-ops.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.tasks/STATUS.md

@@ -1,6 +1,14 @@
 # Task Board
 _Updated: 2026-04-30_
 
+## 🟢 [bootstrap-claude-md-merge] — project-bootstrap upgrade: idempotent merge of canonical CLAUDE.md triggers
+**Status:** done
+**Where I stopped:** Step 5 in `skills/project-bootstrap/SKILL.md` split into Init / Upgrade-merge — upgrade reads existing CLAUDE.md, substring-diffs vs template (case-insensitive trim), platform line preserved if user pinned a non-host platform, asks confirm with diff, appends only missing canonical lines; version bump 1.2.0 → 1.3.0; skill row in `skills/project-bootstrap/README.md` updated to note idempotent merge; root `README.md` + `README.ru.md` upgrade-mode paragraph extended; reinstalled to `~/.claude/skills/project-bootstrap/`, `dist/project-bootstrap.skill` rebuilt; concept page `.wiki/concepts/bootstrap-claude-md-merge.md` written; index + log entries added
+**Next action:** (none — kept until merged)
+**Branch:** master
+
+---
+
 <!--
   Canonical layout. One block per task. Per-task deep context lives in
   .tasks/<task-slug>.md (created by using-tasks when a task becomes active