Add stage-5 phase B: durable single-owner format catalog

Wraps the assign_file scoring core (cluster.jl) in the live catalog the
design's phase B calls for (DESIGN §5B/§9):

- src/catalog.jl: Catalog durable state (frozen-id clusters + sufficient
  stats + processed set + examples); sparse, sidecar-first durable
  save/load; incremental catalog_sweep! (deterministic CRP-predictive
  assignment of new binary/ files); offline compact! that seeds on first
  run and recompacts later; write_nominations! emitting one JSON per
  promotable cluster with a hex magic template.
- bin/cluster_sweep.jl: cron/periodic single-owner runner (--compact
  forces a recluster; first run auto-compacts to seed).
- config.jl: cluster_catalog_path + nominated_dir knobs (FS_CLUSTER_CATALOG,
  FS_NOMINATED_DIR), wired into config_from_env and ensure_dirs.
- Tests: durable round-trip, incremental sweep growth + idempotency,
  §10.1 nothing-from-noise end-to-end (zero promotions), a recurring
  format self-nominating, seed-then-live-assign (165 pass).
- DESIGN_clustering.md: mark phase B built.

bin/cluster_sweep.jl

@@ -0,0 +1,19 @@
+#!/usr/bin/env julia
+#
+# Stage-5 phase-B runner (model/DESIGN_clustering.md §9): the single-owner,
+# periodic/cron process that sweeps `binary/`, folds new files into the durable
+# format catalog by sequential CRP-predictive assignment, and (re)writes
+# promotion nominations. Run it single-threaded on a schedule — it is the ONLY
+# writer of the catalog, so no locking is needed.
+#
+#   julia --project=. bin/cluster_sweep.jl            # incremental live sweep
+#   julia --project=. bin/cluster_sweep.jl --compact  # offline Gibbs (seed / recompact)
+#
+# On a fresh catalog (nothing processed yet) the incremental sweep would send
+# every file to background — there are no clusters to match — so the first run
+# auto-promotes to a compaction pass to seed the catalog. Configure via the
+# FS_CLUSTER_* / FS_NOMINATED_DIR env vars (see src/config.jl).
+
+using FileServer
+
+FileServer.cluster_sweep_cli(ARGS)