refactor(tui): split createTuiChat into chat/ sub-controllers

Extract model-command, questions, and resume sub-machines from the
~1600-line createTuiChat closure into src/chat/ factories that take
explicit dependency bundles (shared ChatChannelDeps/ChannelNotice).
Reorganize src/ so chat/ holds all chat-channel concerns (former input
and session/ files move under it); xml-tool-output moves to components/;
TuiRuntime/TuiResumeHost move to runtime.ts. index.ts drops 2067->~1530
lines. Behavior identical: 167 tests and all TUI snapshots pass unchanged.

packages/ui/tui/tests/xml-tool-output.spec.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { renderUnknownXml } from '../src/xml-tool-output.ts'
+import { renderUnknownXml } from '../src/components/xml-tool-output.ts'
 
 const render = (source: string, limit = 4, expanded = false): string[] | undefined => renderUnknownXml(
   source,