feat(fleet): cross-node bulk label assign with authoritative label discovery (#1389)

* feat(fleet): cross-node bulk label assign with authoritative label discovery

Make Fleet Actions > Bulk label assign work across the fleet. Pick a stack
label that exists anywhere in the fleet, select stacks on one or more nodes,
and the control orchestrates: each target node resolves the label by name,
creating it with the same name and color if missing, then adds it to the
selected stacks while preserving their existing labels. The local node runs
in process; each remote runs its own admin-only local-assign receiver over
the node proxy. Per-node failures (unknown node, no proxy target, unreachable,
mixed-version remote) degrade that node only and are reported per node in the
result. Assignment writes use a transactional INSERT OR IGNORE so the
add-preserve path is idempotent and race-free.

Also make the shared fleet label discovery authoritative: suggestions,
match-preview, and the fleet-stop remote leg now read each node's labels live
over the proxy instead of the control database, which does not mirror remote
labels. A propagated label therefore appears in, and is stoppable by,
Stop-by-label across the fleet, and unreachable nodes are surfaced rather than
silently dropped.

Fleet Actions runs against the unfiltered node list, so overview filters no
longer narrow its scope. The previous node-scoped, replace-by-id bulk-assign
endpoint is removed.

* fix(fleet): treat malformed remote label responses as per-node failures

A 200 response from a remote node whose body is not the expected shape was
treated as a benign empty result, so a malformed remote could read as a clean
zero-stack assign or a "matched, nothing to stop" no-op and even surface a
success toast. Validate the wire shape in the bulk-assign and fleet-stop remote
legs and in the authoritative label discovery fan-out; on a malformed body,
report the node as a per-node failure with the error attributed to its stacks
instead of silently dropping it.

* chore: drop accidentally committed temp file

docs/features/licensing.mdx

@@ -28,7 +28,7 @@ See [the pricing page](https://sencho.io/pricing) for current pricing.
 - Multi-node management in both Proxy and Pilot Agent modes
 - Fleet View with search, sort, filter, and node-card drill-down
 - Manual and scheduled fleet snapshots (create, browse, restore, delete) and Remote OTA node updates (per-node and **Update all**)
-- Actions tab (stop stacks fleet-wide by label, bulk-assign labels to many stacks on a node, prune Docker resources fleet-wide; admin role required), plus fleet-wide bulk Sencho restart
+- Actions tab (stop stacks fleet-wide by label, assign a label to stacks across nodes, prune Docker resources fleet-wide; admin role required), plus fleet-wide bulk Sencho restart
 - Bulk actions on a label (deploy, stop, or restart every stack tagged with it)
 - Atomic deployments with automatic rollback, and one-click rollback to the previous deployment
 - Auto-update policies for stack images and auto-heal policies for failed containers