New-app checklist: reviewed, a gate (onboarding), the wger pilot record, the existing apps' gap page

NEW-APP-CHECKLIST.md: the reviewer's draft reviewed - 60 rows in 10 groups, each with how/why and a since date;
7 rows added, 16 sharpened, 9 wrong claims fixed. onboarding/_TEMPLATE.md (one line per id), onboarding/wger.md
(the pilot, exempt app, 11 open rows each a register row), onboarding/EXISTING-APPS-GAPS.md (read only, from
scripts/onboarding_gaps.py). Gate onboarding (scripts/check-onboarding.py) in --fast: a template directory not
among the 53 published before 2026-10-01 needs a complete record; decoys in test_gate_decoys.py (16 cases, 5 gate
mutants seen red). CLAUDE.md, REUSE.md 5, README point to it. No template changed.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

CONTEXT.md

@@ -2,6 +2,10 @@
 
 > Created with the REUSE.md rollout (2026-07-03). History: `CHANGELOG.md`; format spec: `README.md`.
 
+- **2026-10-01 (evening) — THE NEW-APP CHECKLIST.** `NEW-APP-CHECKLIST.md` (60 rows, `since` per id) + `onboarding/`
+  (`_TEMPLATE.md`, `wger.md` pilot, `EXISTING-APPS-GAPS.md`) + gate `onboarding` (`check-onboarding.py`, `--fast`, decoys).
+  The 53 published apps exempt by name (operator default, may reverse). A new app = template + complete record in one
+  commit. Open from the pilot: R-758..R-764 (R-762/R-763 P2 on wger).
 - **2026-09-24 (morning) — STEP DEFINITIONS (`5ed599c`).** Every ladder entry but the newest has its own compose at
   `templates/<app>/steps/<ladder.step_key(to)>.yml` (sha256 of `to`, canonical JSON, 16 hex = controller
   `stacks.StepKey`); gate rule 4 + decoys; the writer keeps the superseded step; 8 backfilled