feat(tui): token metrics aggregation, plan overlay, tool reasoning, clar dismissal

#295 — include narration_llm tokens in changes-panel aggregate count
#296 — execution plan overlay (Ctrl+P in-session)
#298 — surface reasoning/CoT on tool-call turns in output view
#265 — dismiss clarification modal when answered externally (session.resumed)

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

@@ -66,14 +66,16 @@ const (
 	OverlayHelp
 	OverlayProjectProfile
 	OverlayOperatorProfile
+	OverlayPlan
 )
 
 // RouterEntry is one line in a session's conversation transcript.
 type RouterEntry struct {
-	Role    string // user | router | tool | narration | narration_llm | action
-	Content string
-	Icon    string // action role only: the gutter glyph (✓ ✎ ✗ ⌘ ✕ ⊞ ⊟)
-	Metrics *TurnMetrics
+	Role      string // user | router | tool | narration | narration_llm | action
+	Content   string
+	Icon      string // action role only: the gutter glyph (✓ ✎ ✗ ⌘ ✕ ⊞ ⊟)
+	Metrics   *TurnMetrics
+	Reasoning string // model reasoning/CoT that preceded this entry (tool/artifact turns)
 }
 
 // TurnMetrics carries optional latency + token cost for a ROUTER chat turn.
@@ -440,6 +442,10 @@ type Model struct {
 	// (0 = tail-follow the newest output). PgUp/PgDn + ctrl+u/d move it; esc snaps back.
 	outputScroll int
 
+	// lastReasoning holds the model's reasoning/CoT trace from the most recent
+	// inference.completed, surfaced on the following tool-call and artifact rows.
+	lastReasoning string
+
 	// event-inspector filter (OverlayEventInspector): narrows the event list by a substring
 	// of type/detail. eventFilterTyping is true while the operator is editing the query after /.
 	eventFilter       string