fix(tui): preserve prior segment output on Ctrl+C interrupt

interruptTurn only flushed the in-flight streaming chunk (bufRef) to
the transcript before calling idle(), which wiped segmentMessages and
pendingSegmentTools. Every tool call and commentary line the agent had
already emitted in the current turn disappeared the moment the user
cancelled, even though that output is exactly what they want to keep
when they hit Ctrl+C (quote from the blitz feedback: "everything was
fine up until the point where you wanted to push to main").

Append each flushed segment message to the transcript first, then
render the in-flight partial with the `*[interrupted]*` marker and its
pendingSegmentTools. Sys-level "interrupted" note still fires when
there is nothing to preserve.

ui-tui/src/__tests__/useComposerState.test.ts

@@ -1,11 +1,15 @@
-import { describe, expect, it, vi } from 'vitest'
+import { describe, expect, it } from 'vitest'
 
 import { looksLikeDroppedPath } from '../app/useComposerState.js'
 
 describe('looksLikeDroppedPath', () => {
   it('recognizes macOS screenshot temp paths and file URIs', () => {
-    expect(looksLikeDroppedPath('/var/folders/x/T/TemporaryItems/Screenshot\\ 2026-04-21\\ at\\ 1.04.43 PM.png')).toBe(true)
-    expect(looksLikeDroppedPath('file:///var/folders/x/T/TemporaryItems/Screenshot%202026-04-21%20at%201.04.43%20PM.png')).toBe(true)
+    expect(looksLikeDroppedPath('/var/folders/x/T/TemporaryItems/Screenshot\\ 2026-04-21\\ at\\ 1.04.43 PM.png')).toBe(
+      true
+    )
+    expect(
+      looksLikeDroppedPath('file:///var/folders/x/T/TemporaryItems/Screenshot%202026-04-21%20at%201.04.43%20PM.png')
+    ).toBe(true)
   })
 
   it('rejects normal multiline or plain text paste', () => {