Add scrolling support for menus with many options

[patrick91]

Summary

• Fixes issue where menus break when the terminal screen is not tall enough to contain all options
• Adds automatic scrolling for menus with more options than can fit on screen
• Shows scroll indicators (↑ more / ↓ more) when there are more options above/below
• Reserves consistent space for indicators to prevent UI shifting during navigation

Changes

• menu.py: Added scroll state tracking (scroll_offset, max_visible), scroll helper methods, and scroll indicators
• styles/base.py: Updated render_menu() to render only visible options with scroll indicators
• styles/border.py: Updated render_menu() with same scrolling logic (was missing it entirely)
• examples/scrolling-menu.py: New example demonstrating the scrolling feature

Test plan

• Run uv run pytest tests/ - all tests pass
• Run uv run python examples/scrolling-menu.py to test scrolling interactively
• Test with both TaggedStyle and BorderedStyle
• Test filtering with scrolling (country picker example)
• Verify menu height stays constant during scrolling (no UI shifting)

🤖 Generated with Claude Code

[github-actions]

Thanks for adding the RELEASE.md file!

Below is the changelog that will be used for the release.

---

Add scrolling support for menus with many options.

When a menu has more options than can fit on the terminal screen, it now
automatically scrolls as the user navigates with arrow keys. This prevents
the UI from breaking when the terminal is too small to display all options.

Features:

• Automatic scrolling based on terminal height
• Scroll indicators (↑ more / ↓ more) show when more options exist
• Works with both TaggedStyle and BorderedStyle
• Works with filterable menus (scroll resets when filter changes)
• Optional max_visible parameter for explicit control

Example usage:

from rich_toolkit import RichToolkit
from rich_toolkit.styles.tagged import TaggedStyle

# Auto-scrolling based on terminal height
with RichToolkit(style=TaggedStyle()) as app:
    result = app.ask(
        "Select a country:",
        options=[{"name": country, "value": country} for country in countries],
        allow_filtering=True,
    )

# Or with explicit max_visible limit
from rich_toolkit.menu import Menu

menu = Menu(
    label="Pick an option:",
    options=[{"name": f"Option {i}", "value": i} for i in range(50)],
    max_visible=10,  # Only show 10 options at a time
)
result = menu.ask()

This release was contributed by @patrick91 in #41

[patrick91]

Code looks good! 😊

[github-actions]

This PR was published as 0.17.0