feat(devices): add Reset Stats action for clearing pre-ship QA/bench data

New POST /devices/{id}/reset-stats + ResetStatsModal lets staff clear
QA/bench test data accumulated before a device ships to a customer:
Firestore bell/playback counters and Postgres history tables (logs,
heartbeats, commands, boot events, alert events, ping samples,
diagnostics reports, control/reports, and opt-in live alerts). The two
firmware-side resets (telemetry.reset_boot_data, logs.clear) go over
the existing MQTT command/ack flow instead, since they need the device
online and duplicating that round-trip server-side would just be a
second, inferior implementation.

Also includes two incidental cleanups in devices/router.py: audit-log
entries for create/update now use console_name in their label (missed
by the earlier console_name commit), and add/remove-device-user rename
their local Firestore client from `db` to `fs` to stop shadowing the
`db: AsyncSession` dependency param in the same function scope.
AddDeviceUserModal's results list also gets a max-height + scroll so a
long match list doesn't grow the modal off-screen.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/modals/bellcloud/devices/AddDeviceUserModal.jsx

@@ -172,7 +172,7 @@ export default function AddDeviceUserModal({ open, deviceId, existingUserIds = [
         )}
 
         {/* Results */}
-        <div style={{ display: 'flex', flexDirection: 'column', gap: 'var(--space-2)', minHeight: 80 }}>
+        <div style={{ display: 'flex', flexDirection: 'column', gap: 'var(--space-2)', minHeight: 80, maxHeight: 260, overflowY: 'auto' }}>
           {loading ? (
             <div style={{ display: 'flex', justifyContent: 'center', padding: 'var(--space-6)' }}>
               <Spinner size="sm" />