feat(tui,server,config): live config editor + artifact viewer

Two operator features over the existing WebSocket protocol, plus a tui-go nav fix.

Config editor (g / palette "config"):
- core:config gains a thin registry stack: OrchestrationKnobs ([orchestration]
  block), CorrexConfigWriter (round-trip TOML serializer; parseToml(write(c))==c),
  ConfigHolder (AtomicReference live config), and EditableConfig (allowlist of
  editable fields + patch applier; security fields are absent so they can never
  be patched).
- ConfigService validates -> persists (atomic temp+move) -> swaps the holder ->
  rebuilds config-derived services. Live-apply is scoped to safe seams: stage
  timeout, compaction threshold (now a supplier), router knobs (routerFacade
  rebuild), and personalization/project toggles all take effect on the next
  session/turn; in-flight sessions keep the config they started with.
  server.host/port are persisted + badged "restart required", not hot-swapped.
- Protocol: GetConfig / UpdateConfig / ConfigSnapshot; TUI overlay with
  type-aware editing (bool toggle, enum cycle, inline int/string edit) and save.

Artifact viewer (v / palette "artifacts"):
- Server assembles a session's artifacts from the event log and resolves bytes
  from the CAS store (StreamQueries.listArtifacts) — a replay-neutral snapshot
  read. TUI overlay lists artifacts and shows scrollable content.

tui-go fix: workflow failure no longer clears selectedID (which yanked the user
to the list); listNav lands on the first session when nothing is selected
instead of wrapping to a random one.

Config is not event-sourced (it lives in TOML); editing stays outside the log.

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

@@ -137,9 +137,6 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 		if s := m.session(msg.SessionID); s != nil {
 			s.Active = false
 		}
-		if msg.SessionID == m.selectedID {
-			m.selectedID = ""
-		}
 	case protocol.TypeStageStarted:
 		if s := m.session(msg.SessionID); s != nil {
 			s.CurrentStage = msg.StageID
@@ -277,6 +274,28 @@ func (m *Model) applyServer(msg protocol.ServerMessage) {
 		m.gpuTotalMB = msg.GpuMemoryTotalMb
 		m.gpuUtil = msg.GpuUtilizationPct
 		m.ramMB = msg.ProcessRssMb
+	case protocol.TypeArtifactList:
+		m.artifacts = msg.Artifacts
+		m.artifactsFor = msg.SessionID
+		m.artifactsLoading = false
+		m.artifactScroll = 0
+		if m.artifactsIndex >= len(m.artifacts) {
+			m.artifactsIndex = 0
+		}
+	case protocol.TypeConfigSnapshot:
+		m.configFields = msg.ConfigFields
+		m.configRestart = msg.ConfigRestartRequired
+		m.configLoading = false
+		if msg.ConfigError != nil {
+			m.configError = *msg.ConfigError
+		} else {
+			// A clean snapshot means the staged edits were accepted (or this is a fresh fetch).
+			m.configError = ""
+			m.configStaged = map[string]string{}
+		}
+		if m.configIndex >= len(m.configFields) {
+			m.configIndex = 0
+		}
 	}
 
 	// Background-update badge for non-selected sessions.
@@ -290,7 +309,8 @@ func sessionIDOf(msg protocol.ServerMessage) string {
 	case protocol.TypeStageManifest, protocol.TypeSnapshotComplete,
 		protocol.TypeProtocolError, protocol.TypeProviderStatus,
 		protocol.TypeWorkflowList, protocol.TypeRouterResponse,
-		protocol.TypeModelChanged, protocol.TypeModelList, protocol.TypeResourceStatus:
+		protocol.TypeModelChanged, protocol.TypeModelList, protocol.TypeResourceStatus,
+		protocol.TypeArtifactList, protocol.TypeConfigSnapshot:
 		return ""
 	default:
 		return msg.SessionID