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/components/messageLine.tsx

@@ -1,8 +1,10 @@
 import { Ansi, Box, NoSelect, Text } from '@hermes/ink'
 import { memo } from 'react'
 
-import { LONG_MSG, ROLE } from '../constants.js'
-import { compactPreview, hasAnsi, isPasteBackedText, stripAnsi, userDisplay } from '../lib/text.js'
+import { LONG_MSG } from '../config/limits.js'
+import { userDisplay } from '../domain/messages.js'
+import { ROLE } from '../domain/roles.js'
+import { compactPreview, hasAnsi, isPasteBackedText, stripAnsi } from '../lib/text.js'
 import type { Theme } from '../theme.js'
 import type { DetailsMode, Msg } from '../types.js'