fix: use actual terminal height for scroll instead of hardcoded value

[LuisMIguelFurlanettoSousa]

Summary

Fixes #46

The scroll calculation now uses the actual terminal height instead of a hardcoded visible_height = 10.

Changes

• Added terminal_height: u16 field to AppState (default: 24)
• Updated event loop to set terminal_height from f.size().height each frame
• adjust_scroll now calculates visible height by subtracting UI chrome (breadcrumb, borders, header row, help bar ≈ 8 lines) from the actual terminal height

Before

All terminals → scroll window fixed at 10 lines

After

Terminal with 24 rows → ~16 visible lines
Terminal with 50 rows → ~42 visible lines
Terminal with 12 rows → ~4 visible lines (gracefully handles small terminals)

[abhixdd]

@LuisMIguelFurlanettoSousa Looks good overall, but one issue before merge: scroll height is still hardcoded, so when search/download bars show up, cursor and scroll can get out of sync. Please make adjust_scroll account for those extra rows (or use actual list height), then it’s good.

[LuisMIguelFurlanettoSousa]

@abhixdd Fixed! adjust_scroll now dynamically accounts for the search and download bars:

let mut chrome_height: u16 = 8; // base: breadcrumb + borders + header + help
if self.downloading {
    chrome_height += 2; // download status bar
}
if self.is_searching {
    chrome_height += 3; // search bar with borders
}

This matches the exact Constraint::Length values used in browser.rs layout (download = Length(2), search = Length(3)), so scroll and cursor stay in sync regardless of which bars are visible.

[abhixdd]

@LuisMIguelFurlanettoSousa Thanks for the fix. LGTM! Merging.