chore(deps): bump ratatui 0.30, crossterm 0.29, vt100 0.16

The coupled UI/terminal trio — vt100 0.16 was blocked behind ratatui's
`unicode-width = "=0.2.0"` exact pin, which 0.30 relaxes. Two small
source changes:

* `run_app<B: Backend>` gains a `where io::Error: From<B::Error>` bound.
  ratatui 0.30 made `Terminal::draw` return `Result<_, B::Error>` (the
  backend's associated error type) instead of always `io::Error`. We
  only drive it with `CrosstermBackend` (Error = io::Error), so the
  bound is trivially satisfied and just lets the `?` convert.
* PTY harness `row()`: vt100 0.16's `Cell::contents()` returns `&str`
  (was `String`), so the leading `&` is now a needless borrow.

602 unit + 245 PTY/integration tests pass — including the PTY suite,
which renders the real binary through the upgraded crossterm/ratatui
stack and parses it back via vt100 0.16. clippy `-D warnings` clean.

Author: SamuelSchlesinger