dashboard-v2 (PR 1): design doc + backend read-only endpoints

Kicks off the single-pane-of-glass command-center rewrite. Legacy
/api/* handlers untouched — v2 is additive so cutover is safe.

Doc: docs/dashboard-v2.md — design goals, endpoint spec, cutover
plan.

Backend: new serve_v2 module wired into serve.rs. Endpoints:

  GET /api/v2/node/local/status
  GET /api/v2/node/:name/status         (fan-out: not-yet-impl)
  GET /api/v2/storage/blobs?limit&offset
  GET /api/v2/storage/tags?prefix
  GET /api/v2/storage/refs?limit&offset
  GET /api/v2/storage/snapshots
  GET /api/v2/storage/ref-tracking?repo

V2State opens BlobStore / TagStore / RefStore / SnapshotStore /
RefTracking under the daemon's blob_store_root + the conventional
subdirs (tags-db, refs-db). All handlers are single-node reads;
cross-node fan-out lands in PR 3.

+6 tests: status w/ seeded blob+snapshot, cross-node returns 501,
blobs pagination, tags prefix filter, snapshots list, ref-tracking
repo filter.

395 tests pass. serve.rs merges v2 routes onto the axum router
with shared CORS. Single-shot deploy on tank + architect will
expose /api/v2/* alongside the existing /api/*.

PR 2 = frontend rewrite consuming these endpoints.
PR 3 = fleet fan-out (cross-node aggregation via QUIC RPC).
PR 4 = action endpoints (POST scrub/gc/snapshot/pin).
PR 5 = cutover (deprecate legacy /api/*).

claw-store/src/main.rs

@@ -8,6 +8,7 @@ mod hot;
 mod manifest;
 mod restore;
 mod serve;
+mod serve_v2;
 mod snapshot;
 mod sync;
 mod zfs;