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>

config/coordinator.ts

@@ -90,6 +90,8 @@ export default {
     connections: env.get('PROBE_CONNECTIONS', 6),
     /** Of them, always (its share's minimum; nntpShares). */
     minConnections: env.get('PROBE_MIN_CONNECTIONS', 2),
+    /** No claims while the filesystem under `/` (the NVMe, in the container) has less free (app/services/disk_space.ts). 0: off. */
+    minFreeGb: env.get('PROBE_MIN_FREE_GB', 0),
     /** Candidates claimed at a time. */
     batch: 400,
     /** BODY commands in flight per connection (pipelined; XoverClient.bodies). */