GEN-2907 define run retention eligibility policy - #396

Refs GEN-2907

Delivered

• Added a global 14-day terminal run retention policy, bounded transactional aggregate deletion, and durable retry queues for artifact and provider cleanup.
• Coordinated upload, trace ingestion, finalization, lifecycle delivery, replay, and webhook history with retention; protected active runs and pending automation/verification.
• Added bounded cleanup for independent event histories and temporary records, retained backlog/failure metrics without tenant or run identifiers, dashboard guidance, read-only audit SQL, and staged rollout/recovery documentation.
• Added API/MCP/UI expired-run behavior and browser coverage; fixture teardown now handles expected PostgreSQL 57P01 shutdown events from forced disposable-database cleanup while surfacing other pool errors.
• Production inventory refresh, rollout, deployment, and purge remain separately owned by GEN-2916; this PR performs none of them. GEN-2913 is Canceled and does not block development acceptance.

Validation

Validated exact head 6fe24b20d9011bed83267d573b859d5883c5703a with Node 24.12.0/npm 11.19.0, npm ci, and an isolated local PostgreSQL database. npm test passed: backend 92 files (605 passed, 5 skipped); compiled app/API/PostgreSQL integration (2 passed); Chromium functional tests (7 passed); app unit tests (103 passed, 1 skipped); and proxy checks. git diff --check passed. No production/shared database was used.

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