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/src/config.ts

@@ -10,7 +10,7 @@ import {
   DEFAULT_FILE_SEARCH_EXCLUDED_DIRECTORIES,
   DEFAULT_FILE_SEARCH_MAX_ENTRIES,
   DEFAULT_FILE_SEARCH_MAX_RESULTS,
-} from './file-autocomplete.ts'
+} from './chat/file-autocomplete.ts'
 
 /** Theme and prompt-template settings for the pi-tui terminal mode. */
 export interface TuiThemeConfig {