#378 fix(db): replace the completion path graph load for pg sweep.

Replaces the PostgreSQL completion graph load/sweep with targeted writes for the completed job and its direct dependents. Preserves fail-fast cleanup, attempt retirement, reusable-caller folding, concurrency promotion and run summaries; cancelled siblings lose their assignment/provision rows, and terminal JobSets release their shared holds.

Validation:

• PG-backed control suite on 2cef8991: 233 passed, 0 failed (PostgreSQL 17.11; checkout clean).
• just test-ci last ran on 228ab715 and stopped at fmt-check; a final rustfmt-only adjustment is on e43f88c9 and still needs validation. No full CI green is claimed.

Summary by CodeRabbit

• Bug Fixes
  • PostgreSQL job completion keeps run and job status updates consistent, including when completion reports arrive after cancellation.
  • Fail-fast cancellation applies to all non-terminal sibling jobs and releases their held capacity.
  • Non-terminal job updates no longer store a result value.
  • Dependency handling waits for all required matrix jobs to finish before promoting dependent work.