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/tui.spec.ts

@@ -30,7 +30,7 @@ import {
   type TuiOverlaySession,
   type TuiRuntime,
 } from '../src/index.ts'
-import { WorkspaceFileSearch } from '../src/file-autocomplete.ts'
+import { WorkspaceFileSearch } from '../src/chat/file-autocomplete.ts'
 import {
   appendAssistant,
   appendUser,