Claudinite growth: dedup gcec local pack against the mounted canon

Rebase of PR #736 onto main after #737 (a separate growth-dedup run)
landed overnight and already pruned 3 of its 4 items (one-time git
setup, merge-and-ci's get_check_runs bullet, the divergence-sync
rephrase). This carries only the surviving delta: the squash/(#N)
merge-title bullet restated the canon's default (merge-to-main
SKILL.md step 4, enforced by the blocking squash-merge-history
check) — kept only this repo's genuine divergence, the CI-green-first
(twice for e2e/heavy) gate. README's rules table row updated to match.

Verification: check_the_world.mjs 0 blocking (11 advisory,
pre-existing); npm run test:offline 315/315 passing.

Refs #685

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DnPJ1ngCuAev48BNrQdK5F

Author: claude

.claudinite/local/packs/gcec/README.md

@@ -24,7 +24,7 @@ fingerprinted or seeded.
 | Rule (≤5 words) | How enforced |
 |---|---|
 | test:offline list matches tree | **hardcoded** (`test-offline-list-sync`) |
-| Squash merges, `(#N)` | prose (+ canon squash checks) |
+| CI green before merge (2× heavy) | prose (canon owns method/title) |
 | Generated files: regen, never hand-merge | prose (+ each artifact's own gate) |
 | Branch sync: rebase main + regen | prose |
 | Gallery regenerated → link in chat | prose |

.claudinite/local/packs/gcec/RULES.md

@@ -8,9 +8,10 @@ pipeline" section below, and its two routines live under `dev/routines/`.
 
 ## Working rules
 
-- **Merges to `main` are squash, `(#N)` appended to the title** — a linear,
-  one-commit-per-PR history. CI must be green first (twice for e2e/heavy-browser
-  changes). The project mechanics of driving a merge (dispatching CI in a web
+- **This repo's one divergence from the canon merge recipe: CI must be green
+  first** — twice for e2e/heavy-browser changes. (Merge method and title are the
+  canon default, `squash` with `(#N)`, enforced by the `squash-merge-history`
+  check.) The project mechanics of driving a merge (dispatching CI in a web
   session, the poll back-off, when to arm auto-merge instead of waiting) are the
   merge-and-ci skill — **load it for any PR a session opens**, including one
   opened incidentally mid-task by an unattended run, not only for a deliberate