FleetHealth PR 3: 'Projects' panel — which repos live where

Backend:
* New DashboardProject { repo, cache_bytes, fingerprint_count,
  refs, first_seen_unix, last_seen_unix, tier }.
* Handler build_projects() joins ref-tracking with the ref-store
  and blob-store: for each recorded fp, resolve fp → blob-id via
  RefStore::{get_stamped, get} then sum blob sizes per repo.
* Tier is a wall-clock function of last_seen_unix:
    active < 24h, recent < 7d, else idle.
* DashboardStorageReply gains `projects: Vec<DashboardProject>`
  (serde-default so older clients still parse).

Aggregator:
* New /api/v2/projects endpoint. Fans out DashboardStorage to
  every peer, tags each project row with its originating node,
  returns hottest-first.

Frontend:
* New ProjectsPanel component appended to the FleetHealth
  landing. Groups by repo, one row per project with tier badge
  (active/recent/idle), per-node pill badges, cache-size sum,
  ref list, last-activity age.
* Empty state explains how to populate: claw-cargo build with
  --repo + --git-ref (or CLAWSTOR_REPO/CLAWSTOR_GIT_REF env
  vars in CI).

Data populates automatically as each cache-put runs. Existing
demo entry on tank (clawverse/clawstor · main · c384a4...) will
surface after redeploy.

dashboard-v2/src/pages/CommandCenter.tsx

@@ -1,6 +1,7 @@
 import { useEffect, useState } from 'react';
 import { api, FleetSnapshot, fmtBytes, fmtAge } from '../lib/api';
 import { NodeCard } from '../components/NodeCard';
+import { ProjectsPanel } from '../components/ProjectsPanel';
 
 // FleetHealth landing — human-oriented single-pane-of-glass.
 // Polls the aggregator's /api/v2/fleet every 10 s.
@@ -99,6 +100,8 @@ export function CommandCenter() {
             ))}
         </div>
       </section>
+
+      <ProjectsPanel />
     </div>
   );
 }