Reworks the SPA around the new DashboardStatus fields. The
landing is now a fleet-health dashboard aimed at a layperson —
disk gauges, mount ✓/✗, cache hit rate, next scheduled job.
No hex, no primitives.
Nav restructure:
* Primary: 'Fleet health' (just the landing).
* 'View Advanced ▾' dropdown reveals: Blobs / Tags / Refs /
Snapshots / Ref-tracking. Routes moved under /advanced/*.
New components:
* StorageBar — horizontal used/total bar with pinned/evictable
split, health-color threshold at 60/85%.
* NodeCard — traffic-light dot + disk + hot tier bars + mount
state + cache hit rate + next-timer countdown. Whole card
is a link into node detail.
New CommandCenter:
* Fleet-wide storage roll-up card (sum of every node's disk).
* Grid of NodeCards.
* 10s poll cadence retained from previous version.
Existing StorageBrowser + RefTrackingPage moved behind
/advanced/* routes; internal component code untouched.
