feat: Nessie catalog UI + Iceberg structure explorer + live Data Flow online/offline

Add Project Nessie on lake01 with Command Center Iceberg tab (snapshots,
manifests, data files, time-travel SQL). Data Flow pulses only when endpoints
are reachable; offline nodes/edges render red.

api/main.py

@@ -62,6 +62,7 @@ from lineage import router as lineage_router
 from dq_monitor import router as dq_router
 from observability import router as observability_router
 from catalog_governance import router as governance_router
+from nessie_iceberg import router as nessie_router
 from ssh_terminal import ssh_session
 from node_registry import NODE_IDS, NODE_AGENT, NODE_REGISTRY, is_node_id
 from node_ops import build_node_detail, probe_node, run_node_probe_task
@@ -1044,6 +1045,7 @@ app.include_router(lineage_router)
 app.include_router(dq_router)
 app.include_router(observability_router)
 app.include_router(governance_router)
+app.include_router(nessie_router)
 app.add_middleware(
     CORSMiddleware,
     allow_origins=["*"],