feat(tui): interleave tool rows into live assistant turns

Live turn rendering used to show the streaming assistant text as one
blob with tool calls pooled in a separate section below, so the live
view drifted from the reload view (which threads tool rows inline via
toTranscriptMessages). Model now mirrors reload:

- turnStore gains streamSegments (completed assistant chunks, each
  with any tool rows that landed between its predecessor and itself)
  and streamPendingTools (tool rows waiting for the next chunk)
- turnController.flushStreamingSegment() seals the current bufRef into
  a segment when a new tool.start fires; pending tools get attached to
  that next chunk so order matches reload hydration
- recordMessageComplete returns finalMessages instead of one payload,
  so appendMessage gets the same shape for live-ending turns as for
  reloaded ones
- appLayout renders segments before the progress/streaming area, and
  the streaming message + pending-tools fallback carry whatever tools
  arrived after the last assistant chunk

ui-tui/src/app/turnStore.ts

@@ -1,6 +1,6 @@
 import { atom } from 'nanostores'
 
-import type { ActiveTool, ActivityItem, SubagentProgress } from '../types.js'
+import type { ActiveTool, ActivityItem, Msg, SubagentProgress } from '../types.js'
 
 const buildTurnState = (): TurnState => ({
   activity: [],
@@ -9,6 +9,8 @@ const buildTurnState = (): TurnState => ({
   reasoningActive: false,
   reasoningStreaming: false,
   reasoningTokens: 0,
+  streamPendingTools: [],
+  streamSegments: [],
   streaming: '',
   subagents: [],
   toolTokens: 0,
@@ -32,6 +34,8 @@ export interface TurnState {
   reasoningActive: boolean
   reasoningStreaming: boolean
   reasoningTokens: number
+  streamPendingTools: string[]
+  streamSegments: Msg[]
   streaming: string
   subagents: SubagentProgress[]
   toolTokens: number