feat: rebuild the PostgreSQL query store from JSON source data

[atomantic]

Summary

• Adds a PostgreSQL writer that rebuilds the staged query store directly from the family-tree JSON source, transactionally and idempotently.
• Loads person JSON via a new json-tree-loader, syncs canonical person identities through postgres-person-sync, and writes through a typed postgres-writer surface.
• Wires the rebuild into scripts/rebuild.ts / scripts/index.ts and documents the flow in docs/cli.md and docs/development.md.
• SQLite/JSON stays the live runtime — this only populates the staged PostgreSQL store, so the migration remains reversible.

Test plan

• npm run build -w shared && npm run test:unit — 14 files, 150 tests pass.
• tests/integration/db/postgresWriter.spec.ts covers a full rebuild against a throwaway schema, asserting row counts, canonical identity preservation, and idempotency on a second run. It self-skips unless SPARSETREE_TEST_DATABASE_URL is set.

Closes #149