- Eliminate double terminal::size() call by returning (cols, rows) from
  the check function and passing it to the render function
- Replace println! with write!/queue! inside synchronized update block
  to avoid partial flushes and flickering
- Use display_width() instead of msg.len() for correct horizontal
  centering with multi-byte characters
- Avoid printing newline on the last row to prevent terminal scrolling
- Add unit tests for the minimum size comparison logic
- Use ASCII 'x' instead of Unicode '×' in size display for consistency

Co-Authored-By: Claude Opus 4.5 <[email protected]>

- Use content-based check (msg == title) instead of row index for
  title styling to be robust against message reordering
- Remove explicit array length annotation, let Rust infer it
- Use queue!() consistently instead of mixing execute() and queue!()
  to minimize I/O syscalls within synchronized update block

Co-Authored-By: Claude Opus 4.5 <[email protected]>

When the terminal is too small and the warning screen is shown, only
exit keys (q, Esc, Ctrl+C, Ctrl+D) are accepted. Other key input is
discarded to prevent characters from leaking into the filter or other
browser state.

Previously, the help browser passed 'q' to the filter input (since it
has no separate normal mode), and the history browser could also leak
input when filter mode was active.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

- Cache the too-small check result from the render path in a local flag,
  reusing it in the key handler to avoid a redundant terminal::size()
  syscall on every keypress
- Move feedback_message clearing after the too-small guard in the history
  browser so it is not silently cleared by discarded keypresses

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Move `check_terminal_too_small()` call outside the `if needs_redraw`
block so the flag is always fresh when processing key events, even if a
resize event and key event arrive in the same poll cycle.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Change `let mut too_small = false` to `let mut too_small` since the
variable is always assigned before being read in the loop body.

Co-Authored-By: Claude Opus 4.5 <[email protected]>