fix: banner ASCII art too wide — breaks on small terminals

[VforVitorio]

Problem

The current banner uses a large block-font ASCII art for 'LM → CODE' that
requires ~100+ columns to render correctly. On narrower terminals it wraps
and produces garbled output (see screenshots).

Proposed fix

Two options (pick one or implement both with auto-detection):

A — Smaller ASCII art
Replace the current font with a compact one-line or small figlet-style banner
that fits in ~60 columns:

 _    __  __   ___  ___  ___  ___
| |  |  \/  | / __||_ _||   \| __|
| |__| |\/| || (__  | | | |) | _|
|____|_|  |_| \___||___||___/|___|

or even just styled text: lmcode — local coding agent

B — Responsive banner
Detect terminal width via shutil.get_terminal_size() and:

• width ≥ 100: show current large ASCII art
• width < 100: show compact one-liner

Acceptance criteria

• Banner never wraps or produces garbled output at 80 columns
• Visual identity is still recognisable

[VforVitorio]

Implemented in feat/ui-status-bar. The banner now detects terminal width and falls back to a compact single-line header when the terminal is too narrow to fit the full ASCII art.