[codex] Implement diagnostics push rollout

[cesar-carlos]

Summary

• Add server-side ingestion for agent.autoUpdate.diagnostics.push as an agent-to-hub JSON-RPC notification.
• Persist diagnostics in a dedicated Prisma table with strict validation, feature flags, rate limits, retention, and metrics.
• Harden RPC bridge abort/retry tests and contract alignment while keeping plug_agente updates for a later pass.
• Move E2E communication checks to a nightly/manual workflow.

Validation

• npm run lint
• git diff --check
• Earlier in this branch: npm run typecheck, npm run test:contract, npm run check:openrpc, npm run test, and E2E_TESTS_ENABLED=true npm run test:e2e

Notes

• This is intentionally server-first. The sibling plug_agente repository was not edited in this pass.