dashboard: printer supplies, expiring warranties, mis-numbered bays

Wave one complete. Three cards, no new data and no migrations.

Printer supplies reuses the existing low-supplies query and its five-minute
cache; a Zabbix round-trip per printer on every dashboard load would make this
the slowest page in the app. One row per printer listing every depleted
cartridge, criticals first - a row per cartridge would report one printer three
times and read as three problems, and showing only the worst class would hide a
low cartridge behind a critical one on the same machine when whoever walks out
there wants to carry both.

While there: the low-supplies REPORT itself was including healthy cartridges. A
printer with one empty black and three full colour ones listed all four, so the
reader had to find the problem inside the row. It now lists only what needs
replacing, and the test that asserted the old behaviour now asserts the new.

Expiring warranties keeps already-expired entries on the list rather than
dropping them the day they lapse, which is how they get missed. Horizon is
warranty_expiringdays, default 90, because that suits a site budgeting
quarterly and nobody else.

Mis-numbered bays promotes check-shared-machines out of a CLI command nobody
will remember to run - it found seven bays that had been wrong for weeks. It
reports only numbers with NO child assets, so part markers legitimately sharing
an operation stay silent: that distinction is the whole card, and without it it
would list correct data beside faults and be ignored.

Printers also loses its dead component-named widget; notifications, network and
machines still have theirs.

CHANGELOG.md

@@ -19,8 +19,13 @@ ADR-007 and ADR-002.
   The only evidence a backup still ran was a line in a log file on the PC.
   `lastseenat` is touched on every matching post, including the no-op, and is
   backfilled from the timestamps that already exist.
-- Dashboard cards for enforcement failures, PCs not reporting, and backups that
-  have stopped. The dashboard now renders cards plugins declare, which it never
+- The low-supplies report lists only the cartridges that need replacing. A
+  printer with one empty black and three full colour cartridges was listing all
+  four, so the reader had to hunt for the problem inside the row. The report
+  exists to answer "what needs replacing".
+- Dashboard cards for enforcement failures, machine numbers claimed by two PCs,
+  PCs not reporting, backups that have stopped, printer supplies, and expiring
+  warranties. The dashboard now renders cards plugins declare, which it never
   did before - five plugins had been declaring widgets into a void, pointing at
   components nobody wrote. Cards are ordered by severity, hide themselves when
   there is nothing to report, gate on a permission, and each fetches