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/slash/registry.ts

@@ -0,0 +1,18 @@
+import { coreCommands } from './commands/core.js'
+import { opsCommands } from './commands/ops.js'
+import { sessionCommands } from './commands/session.js'
+import type { SlashCommand } from './types.js'
+
+export const SLASH_COMMANDS: SlashCommand[] = [...coreCommands, ...sessionCommands, ...opsCommands]
+
+const byName = new Map<string, SlashCommand>()
+
+for (const cmd of SLASH_COMMANDS) {
+  byName.set(cmd.name, cmd)
+
+  for (const alias of cmd.aliases ?? []) {
+    byName.set(alias, cmd)
+  }
+}
+
+export const findSlashCommand = (name: string): SlashCommand | undefined => byName.get(name.toLowerCase())