Add E2E terminal tests with expectrl

[bug-ops]

Parent: #542

Problem

No end-to-end tests verify the TUI binary works correctly in a real terminal environment.

Requirements

• Add dev-dependency: expectrl
• Create E2E test harness that spawns cargo run -- --tui in a PTY
• Test scenarios:
  • Startup displays splash screen
  • Basic input/response cycle
  • Quit with 'q' key
• Mark all E2E tests as #[ignore] (requires built binary and optional services)

Acceptance criteria

• At least 3 E2E scenarios passing locally
• Tests are #[ignore] by default, runnable via cargo nextest run -- --ignored