v0.57.0: stable host-storage list + per-app Tier-2 config panel

Part A of the UI-fixes/storage-spike spec.

A1: enrichHostStorageTargets sorts /api/host-metrics storage_targets
server-side and attaches friendly Hungarian labels + purpose, fixing the
#host-storage-bars reorder-on-poll bug. Display labels only — PVE storage
ids are never renamed.

A2: new GET/POST /stacks/{name}/backup Tier-2 config panel; the "2. mentés"
Beállítás button is repointed there from the dead-end deploy page. Customer
can pin a target drive or disable Tier 2; preference is preserved across the
runner's status writes. Always visible (single-SSD + non-HDD apps included).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

controller/internal/agentapi/client.go

@@ -473,6 +473,11 @@ type StorageTarget struct {
 	ClassHint    string        `json:"class_hint"`
 	ThinPool     *ThinPoolFill `json:"thin_pool,omitempty"`
 	Smart        SmartSummary  `json:"smart"`
+	// Label and Purpose are controller-side display enrichment (NOT from the agent): a friendly
+	// Hungarian name + one-line purpose so the customer understands what each storage holds. The
+	// raw PVE storage id stays in Name (display-only labels — we never rename the actual storage).
+	Label   string `json:"label,omitempty"`
+	Purpose string `json:"purpose,omitempty"`
 }
 
 // HostMetricsResponse mirrors the agent's GET /host/metrics payload (host-wide health + per-storage