## Context

`TerminalBounds::num_lines()` uses `floor(height / line_height)` to
compute the terminal grid row count. When the height is derived from `N
* line_height` (as it is for inline/embedded terminals in the Agent
Panel), IEEE 754 float32 arithmetic can produce `N - epsilon` instead of
`N`, causing `floor()` to return `N - 1`. This makes the terminal grid
one row too small, leaving the first line of output in invisible
scrollback (since `display_offset = 0`). The same issue applies to
`num_columns()`.

The fix adds a small tolerance (`0.01`) before flooring, which absorbs
float precision errors without affecting genuine fractional results.

Closes #51609

## How to Review

Small PR — focus on the tolerance value (`0.01`) in `num_lines()` and
`num_columns()` in `crates/terminal/src/terminal.rs`. The two new tests
(`test_num_lines_float_precision`, `test_num_columns_float_precision`)
verify the fix across 1,000+ float combinations that previously
triggered the bug.

## Self-Review Checklist

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Fixed the first line of terminal output sometimes missing in Agent
Panel terminal blocks.