feat: add ratatui TUI with interactive process monitor (ISSUE-035)

[proboscis]

Summary

• Implements Phase 1-3 of ISSUE-035: Ratatui TUI for enhanced CLI experience
• Adds runbox monitor command for interactive process monitoring
• Adds interactive log viewer with scrollback, search, and follow mode

Changes

New Dependencies (crates/runbox-cli/Cargo.toml)

• ratatui 0.28 (terminal UI framework)
• crossterm 0.28 (terminal backend)
• tokio (async runtime for events)
• futures, libc

New TUI Module (crates/runbox-cli/src/tui/)

• mod.rs - Module exports
• app.rs - Main application state and event loop
• event.rs - Keyboard/tick event handling
• ui.rs - Common UI components (colors, styles, helpers)
• views/monitor.rs - Process monitor view
• views/logs.rs - Log viewer view

New Command

• runbox monitor [--tick-rate <secs>] - Interactive process monitor

Features Implemented

Process Monitor (runbox monitor)

• Real-time process list with auto-refresh (configurable tick rate)
• Keyboard navigation (j/k or arrows)
• Color-coded status (green=running, blue=done, red=failed)
• Actions on selected process:
  • Enter: View logs
  • s: Stop running process
  • a: Attach to tmux/zellij session
  • r: Manual refresh
  • q: Quit

Interactive Log Viewer

• Scrollback with vim-style navigation (j/k, g/G, Page Up/Down)
• Search with / (vim-style) with n/N for next/prev match
• Follow mode (f) for auto-scroll to new content
• Highlighted search matches

Testing

• All existing tests pass
• cargo build --package runbox-cli succeeds
• cargo test --package runbox-cli passes
• runbox monitor --help displays correct usage

Related Issue

ISSUE-035: Ratatui TUI for enhanced CLI experience

Future Phases (not in this PR)

• Phase 4: Runnable browser (runbox list --tui)
• Phase 5: Dashboard with split-pane layout