fix(tui): render full resume modal height without clipping rows

[Acters]

This PR fixes an off-by-one rendering issue in the resume modal where one selectable session row could be hidden.

When a non-auto modal view (like the resume picker) was rendered, the bottom pane still reserved composer padding, which reduced the visible view height by one row. That caused:

• A single resumable session to be selectable but not visibly rendered.
• N resumable sessions to show only N-1 visible rows.

What changed

• Removed bottom-padding subtraction for non-auto modal views so they consume the full available modal height.
• Kept existing behavior for auto coordinator views and composer layout.
• Added a regression test that verifies a single resume row is visible at desired height.

Files changed

• code-rs/tui/src/bottom_pane/mod.rs

Validation

• cargo test -p code-tui bottom_pane::tests::resume_selection_renders_single_row_at_desired_height

fixes #542