Introduce a new CI workflow that exercises the config-in-database read/write
path end-to-end. Unlike `live-tests.yml`, this workflow has no batch_writes
matrix: it boots Postgres, stores the Postgres live-tests config glob via
`gateway --store-config`, then runs the full live suite against a gateway
booted from the database with `TENSORZERO_INTERNAL_FLAG_ENABLE_CONFIG_IN_DATABASE=true`.

Unfortunately these tests need to run serially because concurrent edits conflict;
I don't think we can get around this.

Add e2e tests for config-editing PR #7185 review fixes

Covers the three behavioral fixes from the PR review:

- `test_config_editing_apply_persists_transitive_include_templates`:
  regression test for the Codex P1 — after applying a config whose
  template transitively includes a filesystem-backed template via
  MiniJinja `{% include %}`, the discovered template must be persisted
  in `stored_files` with the `ui-config-editor` creation source.
  Without the `write_stored_config_in_tx` merge fix, the row is never
  written and a reload from stored-config tables on a fresh gateway
  would break. Also sanity-checks the rendered system prompt on a
  downstream inference.

- `test_config_editing_validate_accepts_transitive_include`: exercises
  the validate endpoint's happy path for filesystem discovery (the
  client-side precheck before `Apply` is clicked).

- `test_config_editing_cas_rejects_stale_base_signature_for_new_edit`:
  after the CAS check simplification (removal of the
  `canonical_signature` short-circuit), a new edit built on top of a
  stale `base_signature` must still 409.

Also updates the no-op apply test's doc comment now that the
special-case short-circuit has been removed, and fixes stale
`config::` imports to `config_toml::`.