Stack 1 of 7 for the research child-document redesign.

Adds ordinary child-channel relationships, atomic publication of completed research into initialized child documents, immediate inline research request startup, durable retry/reconciliation behavior, and migrations 012–014 after main’s document-description migration.

This layer preserves the existing user-facing Research Workspace while establishing the backend contract used by later stack layers.

Verification: - Focused storage, channel, research service, and route tests: 49 passed - bun test: 1,267 passed; 2 PostgreSQL skips; socket suite rerun with bind permission: 11 passed - bun run types - bun run ci - git diff --check