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.

src/FileServer.jl

@@ -19,7 +19,8 @@ include("classify.jl")  # Classifier + load_classifier/classify (needs model.jl)
 include("metadata.jl")  # exiftool extraction + sidecar enrichment (stage 2)
 include("content.jl")   # binary-vs-text triage for unknown files (stage 3)
 include("language.jl")  # natural + programming language enrichment for text (stage 4)
-include("cluster.jl")   # unknown-format discovery by header clustering (stage 5)
+include("cluster.jl")   # unknown-format discovery by header clustering (stage 5, science)
+include("catalog.jl")   # durable single-owner format catalog (stage 5, phase B; needs cluster.jl + metadata.jl fsync)
 include("worker.jl")
 
 # Globals the HTTP handlers read at request time. Set once in `run`, before the