* feat(channels): share inbound webhook dedupe across pods via Postgres (#4120)
* ci: run cross-pod inbound dedupe integration tests in CI
Expose the job Postgres service via DEDUPE_TEST_POSTGRES_URL so the integration tests (issue #4120) actually execute instead of silently skipping. Normalize the URL for asyncpg (postgresql:// -> +asyncpg, drop libpq-only sslmode) and await the now-async _is_duplicate_inbound in test_github_dispatcher.
Enforce one queued or running scheduled-task run per task with a partial unique index. The migration resolves legacy duplicates before creating the index, and losing inserts use the existing conflict or skip outcomes.
