fix(tui): slash.exec _pending_input commands, tool ANSI, terminal title

Additional TUI fixes discovered in the same audit:

1. /plan slash command was silently lost — process_command() queues the
   plan skill invocation onto _pending_input which nobody reads in the
   slash worker subprocess.  Now intercepted in slash.exec and routed
   through command.dispatch with a new 'send' dispatch type.

   Same interception added for /retry, /queue, /steer as safety nets
   (these already have correct TUI-local handlers in core.ts, but the
   server-side guard prevents regressions if the local handler is
   bypassed).

2. Tool results were stripping ANSI escape codes — the messageLine
   component used stripAnsi() + plain <Text> for tool role messages,
   losing all color/styling from terminal, search_files, etc.  Now
   uses <Ansi> component (already imported) when ANSI is detected.

3. Terminal tab title now shows model + busy status via useTerminalTitle
   hook from @hermes/ink (was never used).  Users can identify Hermes
   tabs and see at a glance whether the agent is busy or ready.

4. Added 'send' variant to CommandDispatchResponse type + asCommandDispatch
   parser + createSlashHandler handler for commands that need to inject
   a message into the conversation (plan, queue fallback, steer fallback).

ui-tui/src/types/hermes-ink.d.ts

@@ -93,6 +93,7 @@ declare module '@hermes/ink' {
   export function useHasSelection(): boolean
   export function useStdout(): { readonly stdout?: NodeJS.WriteStream }
   export function useTerminalFocus(): boolean
+  export function useTerminalTitle(title: string | null): void
   export function useDeclaredCursor(args: {
     readonly line: number
     readonly column: number