test: e2e init capture against testcontainers postgres

Spins up postgres, seeds a small schema + ANALYZE, then runs the built
`dryrun init --db` binary in a tempdir and asserts schema.json,
history.db, and the round-tripped annotated snapshot (schema + planner +
primary activity) all land. Marked `#[ignore]` so it stays opt-in.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: radim