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/update.go

@@ -144,6 +144,8 @@ func (m Model) handleNormalKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 		m.overlayEventIdx = 0
 	case "t":
 		m.overlay = OverlayToolPalette
+	case "m":
+		m.openModelsOverlay()
 	case "w":
 		if ds == StateIdle {
 			m.wfVisible = !m.wfVisible
@@ -333,10 +335,43 @@ func (m Model) handleOverlayKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 		if runeIs(k, "t") {
 			m.overlay = OverlayNone
 		}
+	case OverlayModels:
+		switch {
+		case k.Type == tea.KeyUp || runeIs(k, "k"):
+			if m.modelsIndex > 0 {
+				m.modelsIndex--
+			}
+		case k.Type == tea.KeyDown || runeIs(k, "j"):
+			if m.modelsIndex < len(m.availableModels)-1 {
+				m.modelsIndex++
+			}
+		case k.Type == tea.KeyEnter:
+			if m.modelsIndex >= 0 && m.modelsIndex < len(m.availableModels) {
+				m.client.Send(protocol.SwapModel(m.availableModels[m.modelsIndex]))
+				m.overlay = OverlayNone
+			}
+		case runeIs(k, "c"):
+			m.client.Send(protocol.ClearModelPin())
+			m.overlay = OverlayNone
+		case runeIs(k, "m"):
+			m.overlay = OverlayNone
+		}
 	}
 	return m, nil
 }
 
+// openModelsOverlay opens the model picker, pre-selecting the resident model.
+func (m *Model) openModelsOverlay() {
+	m.overlay = OverlayModels
+	m.modelsIndex = 0
+	for i, id := range m.availableModels {
+		if id == m.currentModel {
+			m.modelsIndex = i
+			break
+		}
+	}
+}
+
 func runeIs(k tea.KeyMsg, s string) bool {
 	return k.Type == tea.KeyRunes && string(k.Runes) == s
 }
@@ -374,6 +409,7 @@ func paletteCommands() []paletteCmd {
 	return []paletteCmd{
 		{"workflows", "start workflow", "open the workflow picker"},
 		{"tools", "tool palette", "tools for the current stage"},
+		{"models", "swap model", "pick / pin the local model"},
 		{"events", "event inspector", "browse the event stream"},
 		{"mode", "toggle mode", "switch chat / steering"},
 		{"cancel", "cancel session", "stop the selected session"},
@@ -404,6 +440,8 @@ func (m Model) execPalette(id string) (tea.Model, tea.Cmd) {
 		m.wfIndex = 0
 	case "tools":
 		m.overlay = OverlayToolPalette
+	case "models":
+		m.openModelsOverlay()
 	case "events":
 		m.overlay = OverlayEventInspector
 		m.overlayEventIdx = 0