feat: correx-managed model lifecycle slice 5 — Go TUI model swap + telemetry

Go TUI decodes model.changed / model.list / resource.status and renders a
status-bar VRAM/GPU%/RAM gauge plus a models overlay (m key / palette 'models'):
lists configured models with the resident one marked, enter swaps (SwapModel),
c clears the pin (ClearModelPin). All three new server messages are
non-event-bearing control/gauge frames, applied immediately like
provider.status_changed.

Server addition required for the picker: ServerMessage.ModelList (model.list,
NonEventMessage) sent once in the initial snapshot from
ManagedInferenceRouter.availableModelIds()/currentModelId() — the TUI otherwise
cannot enumerate swap targets.

Completes the 5-slice model-lifecycle feature. ./gradlew check green; go build/vet clean.

Plan: docs/plans/2026-05-31-model-lifecycle-management.md (slice 5 of 5).

apps/tui-go/internal/app/model.go

@@ -45,6 +45,7 @@ const (
 	OverlayEventInspector
 	OverlayDiff
 	OverlayToolPalette
+	OverlayModels
 )
 
 // RouterEntry is one line in a session's conversation transcript.
@@ -158,6 +159,14 @@ type Model struct {
 	currentModel string
 	providerType string // LOCAL | REMOTE
 
+	// managed-model swap (nil resource fields = unavailable)
+	availableModels []string
+	modelsIndex     int
+	gpuUsedMB       *int64
+	gpuTotalMB      *int64
+	gpuUtil         *int
+	ramMB           *int64
+
 	// diff / overlay
 	overlay          OverlayKind
 	overlayEventIdx  int