Merge NEXT: planning, generation map and portable configuration on top of the OIDC access model

NEXT predates the access work, so the identity layer follows master: access comes from
configured groups, instance administrators replace the site administration, and accounts are
created by SSO or by an administrator. Kept from NEXT: manual publication with the Review
changes panel and shared generator drafts, portable import/export (meguri/v2), the layered
generation map with binding provenance, JSM provider changes, contact/approval semantics and
the account-owned Person. Dropped: site administration, local sign-up, and the mandatory
unique email with its contact/account migrations. The manual-publication migration is
renumbered m_0010 after m_0009_access.

Accounts without an email still get a Person in every workspace they reach, a changed sign-in
email updates the account's person, and an account that loses access keeps its linked person so
schedules stay valid. Instance administrators may use Sync and shared drafts.

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/check.yml

@@ -53,7 +53,7 @@ jobs:
         env:
           DATABASE_URL: postgresql://postgres:test-only@postgres:5432/meguri_test
           MEGURI_SEED_DEMO: "true"
-          MEGURI_DEMO_SANDBOXES: "12"
+          MEGURI_DEMO_SANDBOXES: "14"
           MEGURI_BROWSER_CHANNEL: chromium
         run: |
           cargo build --locked