Make `resume` work without `<sessionId>` by opening the TUI directly on the session manager screen, using a `LaunchOptions` object to pass both `sessionId` and `initialScreen`.

Changes:

1. `src/tui.tsx`

- Change `renderApp(sessionId?: string)` → `renderApp(options: LaunchOptions = {})`.
- Pass `options.sessionId` and `options.initialScreen` through to `<App>`.
- `screen.setClearHandler` rerender: pass `{ sessionId: nextSessionId ?? options.sessionId }` (drop `initialScreen` on rerender — resets to chat).

2. `src/components/App/App.tsx`

- Change `Props` from `{ sessionId?: string }` → `{ sessionId?: string; initialScreen?: Screen }`.
- Pass `initialScreen` to `useScreenRouter`.

3. `src/components/App/hooks/useScreenRouter.ts`

- Accept `initialScreen?: Screen` param.
- Change `useState<Screen>(SCREEN.CHAT)` → `useState<Screen>(initialScreen ?? SCREEN.CHAT)`.

4. `src/cli.ts`

- Import `{ SCREEN } from './constants'` and `type { Screen } from './types'`.
- Define `interface LaunchOptions { sessionId?: string; initialScreen?: Screen }`.
- Change `'resume <sessionId>'` → `'resume [sessionId]'` (optional arg).
- Update action: if `sessionId` provided, load + validate as today; if absent, `launchTui({ initialScreen: SCREEN.SESSION_MANAGER })`.
- Change `launchTui(sessionId?: string)` → `launchTui(options: LaunchOptions = {})`, pass `options` to `renderApp`.

5. Tests

**`src/cli.test.ts`**

- Update `ResumeAction` type: `(sessionId?: string) => Promise<void>`.
- Update existing `renderApp` call assertions: `renderApp('session-1')` → `renderApp({ sessionId: 'session-1' })`.
- Update no-args TUI test: `renderApp(undefined)` → `renderApp({})`.
- Add: `resume` with no `sessionId` → `renderApp({ initialScreen: SCREEN.SESSION_MANAGER })`, no `loadSession` call.

**`src/tui.test.tsx`**

- Update `renderApp()` call → `renderApp({})` (or keep no-arg if default param is used).
- Verify `App` receives correct props for both `sessionId` and `initialScreen` paths.

**`src/components/App/hooks/useScreenRouter.test.ts`** _(if it exists)_

- Add a test for `initialScreen: SCREEN.SESSION_MANAGER` starting on that screen.