Dashboard: rebuild into an operator cockpit (0.38.0)

Replace the analytics-style dashboard (stack-health funnel, uptime %,
operations/day grid, AI pill) with an attention-driven fleet cockpit:

- New /api/dashboard/fleet endpoint: server-side fan-out across the local
  host and every agent into one payload — a prioritized "needs attention"
  list, headline KPIs, an honest stack-status breakdown and a per-host
  resource rollup. Each agent uses its own DB session so the fan-out is
  concurrency-safe; failures degrade to "offline" instead of stalling.
- New frontend: AttentionStrip, FleetKpiRow, StackStatusBar and
  HostResourceTable; Dashboard.tsx rewritten around them.
- Remove the funnel/summary endpoints, the uptime sampler loop and the
  ops-activity machinery; delete the now-unused chart components.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/routers/dashboard.py

@@ -1,4 +1,4 @@
-"""Dashboard aggregation endpoints (funnel + summary widgets)."""
+"""Dashboard aggregation endpoint (fleet-wide cockpit data)."""
 from __future__ import annotations
 
 from fastapi import APIRouter, Depends
@@ -12,18 +12,12 @@ from services import dashboard_service
 router = APIRouter(prefix="/api/dashboard", tags=["dashboard"])
 
 
-@router.get("/funnel")
-async def funnel(
+@router.get("/fleet")
+async def fleet(
     refresh: bool = False,
     session: Session = Depends(get_session),
     _user: User = Depends(get_current_user),
 ) -> dict:
-    return await dashboard_service.compute_funnel(session, refresh=refresh)
-
-
-@router.get("/summary")
-async def summary(
-    session: Session = Depends(get_session),
-    _user: User = Depends(get_current_user),
-) -> dict:
-    return await dashboard_service.compute_summary(session)
+    """Fleet-wide 'needs attention' list, KPIs and per-host rollup across the
+    local host and every agent — the data behind the operator cockpit."""
+    return await dashboard_service.compute_fleet(session, refresh=refresh)