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/app/turnStore.ts

@@ -0,0 +1,47 @@
+import { atom } from 'nanostores'
+
+import type { ActiveTool, ActivityItem, SubagentProgress } from '../types.js'
+
+export interface TurnState {
+  activity: ActivityItem[]
+  reasoning: string
+  reasoningActive: boolean
+  reasoningStreaming: boolean
+  reasoningTokens: number
+  streaming: string
+  subagents: SubagentProgress[]
+  toolTokens: number
+  tools: ActiveTool[]
+  turnTrail: string[]
+}
+
+function buildTurnState(): TurnState {
+  return {
+    activity: [],
+    reasoning: '',
+    reasoningActive: false,
+    reasoningStreaming: false,
+    reasoningTokens: 0,
+    streaming: '',
+    subagents: [],
+    toolTokens: 0,
+    tools: [],
+    turnTrail: []
+  }
+}
+
+export const $turnState = atom<TurnState>(buildTurnState())
+
+export const getTurnState = () => $turnState.get()
+
+export const patchTurnState = (next: Partial<TurnState> | ((state: TurnState) => TurnState)) => {
+  if (typeof next === 'function') {
+    $turnState.set(next($turnState.get()))
+
+    return
+  }
+
+  $turnState.set({ ...$turnState.get(), ...next })
+}
+
+export const resetTurnState = () => $turnState.set(buildTurnState())