fix(deployment): align Neon root cutover automation

[xiaoland]

What changed

• record the completed Neon project-root migration and the new root/default production topology
• reset a sanitized preview-base clone from production to runtime identity before PR branches inherit it
• make preview and production Heroku delivery accept an already-running identical container image as an idempotent no-op
• document the encrypted restore, recovery branch, preview lineage, retired project, and operational invariants

Why

The project migration removed the provider-required legacy master ancestry by moving production into a new Neon project whose root is production. During cutover, two pre-existing automation assumptions surfaced:

1. a copied preview-base retained the immutable production database identity even after its application rows were sanitized, so preview bootstrap correctly refused it
2. Heroku may decline to create a new release when the exact image is already running, while delivery incorrectly required every release command to increment the release version

Impact

• production and open PR previews already run on the new Neon project
• future preview-base replacement is atomic, data-free, and bootstrap-compatible
• repeated delivery of an identical image no longer reports a false failure
• no credential or production row data is committed

Validation

• Ruff: passed
• Pyrefly: 0 diagnostics
• targeted Pytest suite: 23 passed
• preview and production composite Action YAML: parsed successfully
• migration evidence: matching value-free manifests and normalized schema dumps
• production and rebuilt preview Core readiness: HTTP 200
• production and PR feat(extension): add Twitter setup wizard backend #52 PostgREST read/write/JWT denial contract: passed