Build the FIRSTTOUCH overflow trigger flagged in FABRIC-2.md §I.2

The overflow-triggered migration path (a WIREBIND-attached identity's own
drive running low on space) was scoped but never built -- only the
trigger-detection call site was missing, per this section's own text.

- capsule_wirebind.c now tracks the attached blkio_dev* alongside the
  already-tracked VM id, set in try_attach() and cleared in both
  EJECT/UNCLEAN paths.
- New capsule_wirebind_overflow_idle_check(), called once per idle tick
  in repl.c right alongside blk_migration_idle_check() (same cadence):
  reads the attached drive's free/total via blk_get_device_free_blocks(),
  and if free space is below a fixed 10% threshold, extends the
  identity's pool with a one-time blk_firsttouch_claim() of 8 additional
  devblocks on Artemis's system-resident device.
- New blk_owner_has_claim(owner_fp) in block_subsystem.c answers the
  debounce question blk_firsttouch_claim()'s own doc comment had left
  open: a disk scan, not a RAM flag, so the already-extended answer
  survives reboot/reattach, matching BMAPFMT's "ownership travels with
  the block" model.

Premise checked before building (does a WIREBIND-attached drive actually
give a real free/total signal, or does it stay PROVISIONAL/raw): traced
repl.c's attach sequence and confirmed blk_subsys_attach_device() runs on
the same dev pointer right after WIREBIND, and a WIREBIND-eligible drive
is always already STFR/v2-formatted, so the signal is real. Premise held,
unlike the BAM item's overstated one.

Verified with the mandatory 3-arch QEMU acceptance (identical dictionary
hashes, no regression) plus a live logic test of blk_owner_has_claim():
a temporary TEST-OWNER-CLAIM word, run once via SK_CMD and reverted,
confirmed it correctly detects the claiming owner and rejects an
unrelated one. The low-disk-space-triggers-a-claim path itself is not
verified end-to-end -- that needs a real minted WIREBIND-user thumbdrive
with deliberately tiny capacity, out of scope for this pass; noted as
such in the FABRIC-2.md §I.2 closure note rather than overclaimed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018EjXFo7mPXjUMjfJeuUUz4

src/starkernel/repl.c

@@ -368,6 +368,13 @@ static void sk_repl_idle(VM *active_vm)
      * migration, needs a call site threaded from WIREBIND). */
     blk_migration_idle_check();
 
+    /* FABRIC-2.md §I.2's own overflow trigger, closed 2026-09-05: the
+     * call site named above, now built. Same cadence, same idle-tick
+     * neighbor -- see capsule_wirebind_overflow_idle_check()'s own doc
+     * comment for what it does and why it's a one-time extension, not a
+     * growth loop. */
+    capsule_wirebind_overflow_idle_check();
+
     /* FABRIC-2.md Phase C (2026-08-28): distributed messaging pump. Every
      * live VM except Hera herself now owns its own MSG-ARENA/CH-ARENA and
      * MSG-TICK word (see capsules/common/messaging.4th) instead of only