Prober: no claims under PROBE_MIN_FREE_GB free on the NVMe

At ~200 articles/s what the prober stores (inspections, par2 file lists,
the WAL) took ~0.8-1.1 GB an hour of homelab's root, and nothing stopped it
at the 10 GB floor. Below 12 GB free it claims nothing (resumed 1 GB above):
the lanes go dry and its share shrinks to its minimum.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/compose.yaml

@@ -130,6 +130,9 @@ services:
     environment:
       <<: *app-env
       PROBE_CONNECTIONS: ${PROBE_CONNECTIONS:-8}
+      # No claims under this much free on the NVMe (its overlay root): 2 GB above the 10 GB floor, for what the
+      # tail, the merger and the judge write meanwhile.
+      PROBE_MIN_FREE_GB: ${PROBE_MIN_FREE_GB:-12}
 
   # The par2 merge: releases whose files one par2 set describes (what the prober read) become one. No NNTP.
   merger: