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/model.go

@@ -47,6 +47,8 @@ const (
 	OverlayDiff
 	OverlayToolPalette
 	OverlayModels
+	OverlayArtifacts
+	OverlayConfig
 )
 
 // RouterEntry is one line in a session's conversation transcript.
@@ -188,6 +190,23 @@ type Model struct {
 	diffScrollOffset int
 	eventStripShown  bool
 
+	// artifact viewer (OverlayArtifacts) — populated by the artifact.list response
+	artifacts        []protocol.ArtifactDto
+	artifactsFor     string // sessionId the current listing belongs to
+	artifactsIndex   int
+	artifactScroll   int
+	artifactsLoading bool
+
+	// config editor (OverlayConfig) — populated by the config.snapshot response
+	configFields  []protocol.ConfigFieldDto
+	configIndex   int
+	configStaged  map[string]string // key -> edited value, pending save
+	configEditing bool              // true while typing a value into configEditBuf
+	configEditBuf string
+	configError   string
+	configRestart []string // keys from the last save that need a restart
+	configLoading bool
+
 	// command palette
 	paletteFilter string
 	paletteIndex  int
@@ -214,6 +233,7 @@ func NewModel(client *ws.Client) Model {
 		history:         map[string][]string{},
 		historyIndex:    -1,
 		routerMessages:  map[string][]RouterEntry{},
+		configStaged:    map[string]string{},
 		chatMode:        ChatModeChat,
 		providerType:    "LOCAL",
 		snapshotPhase:   true,