feat(agents): full implementation of harness engineering and file sync fixes ...

- Implemented Area 1: Backend scaffolding, CRUD, schemas, and session locking
- Implemented Area 2: Agent execution loop, RAG integration, and Circuit Breaker
- Updated UI: Configure CRON triggers, Target Mesh nodes, and display system prompt in Agent Drilldown
- Fixed LLM fallback resolving vertex_ai_beta
- Fixed File System Sync pseudo-nodes (hub, local) raising 'Offline'
- Fixed FileSystemNavigator initialPath bug causing synced files not to render in UI Mesh Workspace

Fix gigabyte file sync race conditions and malicious path errors

Fix file sync integration tests and session auto-purge bug

Refactor integration tests, introduce CUJ isolation, create E2E mesh runner script with no-rebuild, and clean up orphan files

chore: remove hardcoded prod passwords from test scripts and workflows

fix: resolve file sync infinite bounce loop and unbound local variable bugs

fix: cat() on deleted file returns instantly instead of timing out ...

Root cause: two separate silent-failure bugs caused 15s stalls on file-not-found:

1. agent-node/node.py _push_file(): when a READ arrives for a missing file,
   silently returned without sending any response. The Hub journal sat waiting
   for the full 15s timeout.
   Fix: send ERROR SyncStatus back immediately with task_id so the journal
   resolves at once.

2. ai-hub/assistant.py cat(): after the mirror fast-path found no file, it
   fell through and sent a READ gRPC to the node anyway, compounding the wait.
   Fix: short-circuit with {error: File not found} when the file is absent
   from the session mirror — no node round-trip needed.

test: added Case 9 (TestSmallFileSync) — asserts that cat() on a freshly
deleted file resolves in < 3s on both nodes (guard against regression).

fix(integration_tests): correct API paths to /api/v1/ and make USER_ID env-configurable ...

- SESSIONS_PATH and NODES_PATH now include /api/v1/ prefix matching production
- USER_ID reads from SYNC_TEST_USER_ID env var (required to pass node access checks)
- All 8 file sync tests pass against live production (verified via SSH)

test: add file sync integration test suite (cases 1-8) ...

Covers all 8 real-world file sync scenarios:
  Cases 1-4 (small files):
  1. Write from node-1 → node-2 + server mirror receive it
  2. Write from server (via node-1) → all client nodes receive it
  3. Delete from server → all client nodes purged
  4. Delete from node-2 → server mirror + node-1 purged

  Cases 5-8 (20 MB large files, multi-chunk):
  5-8: Same cases as above but with 20 MB files to exercise multi-chunk sync

  Design:
  - Synchronous httpx client (no asyncio overhead)
  - Shared module-scoped swarm_control session with both nodes attached
  - _poll_until() helper for timeout-based convergence checks
  - Auto-skip via requires_nodes marker when Hub/nodes are unreachable
  - Env vars: SYNC_TEST_BASE_URL, SYNC_TEST_NODE1, SYNC_TEST_NODE2