refactor(tui): store-driven turn state + slash registry + module split

Hoist turn state from a 286-line hook into $turnState atom + turnController
singleton. createGatewayEventHandler becomes a typed dispatch over the
controller; its ctx shrinks from 30 fields to 5. Event-handler refs and 16
threaded actions are gone.

Fold three createSlash*Handler factories into a data-driven SlashCommand[]
registry under slash/commands/{core,session,ops}.ts. Aliases are data;
findSlashCommand does name+alias lookup. Shared guarded/guardedErr combinator
in slash/guarded.ts.

Split constants.ts + app/helpers.ts into config/ (timing/limits/env),
content/ (faces/placeholders/hotkeys/verbs/charms/fortunes), domain/ (roles/
details/messages/paths/slash/viewport/usage), protocol/ (interpolation/paste).

Type every RPC response in gatewayTypes.ts (26 new interfaces); drop all
`(r: any)` across slash + main app.

Shrink useMainApp from 1216 -> 646 lines by extracting useSessionLifecycle,
useSubmission, useConfigSync. Add <Fg> themed primitive and strip ~50
`as any` color casts.

Tests: 50 passing. Build + type-check clean.

ui-tui/src/content/hotkeys.ts

@@ -0,0 +1,19 @@
+export const HOTKEYS: [string, string][] = [
+  ['Ctrl+C', 'interrupt / clear draft / exit'],
+  ['Ctrl+D', 'exit'],
+  ['Ctrl+G', 'open $EDITOR for prompt'],
+  ['Ctrl+L', 'new session (clear)'],
+  ['Alt+V / /paste', 'paste clipboard image'],
+  ['Tab', 'apply completion'],
+  ['↑/↓', 'completions / queue edit / history'],
+  ['Ctrl+A/E', 'home / end of line'],
+  ['Ctrl+Z / Ctrl+Y', 'undo / redo input edits'],
+  ['Ctrl+W', 'delete word'],
+  ['Ctrl+U/K', 'delete to start / end'],
+  ['Ctrl+←/→', 'jump word'],
+  ['Home/End', 'start / end of line'],
+  ['Shift+Enter / Alt+Enter', 'insert newline'],
+  ['\\+Enter', 'multi-line continuation (fallback)'],
+  ['!cmd', 'run shell command'],
+  ['{!cmd}', 'interpolate shell output inline']
+]