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>

README.md

@@ -58,7 +58,10 @@ project's folder and it will, in one pass:
 
 Two modes, picked automatically: **init** for an empty folder, **upgrade**
 for an existing project (the skill only fills the gaps and never overwrites
-without explicit confirmation).
+without explicit confirmation). On upgrade, `CLAUDE.md` is merged
+idempotently — only canonical trigger lines that aren't already present are
+appended after explicit confirm, so re-running `project-bootstrap` after a
+template change picks up the new triggers without duplicating the old ones.
 
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