fix(fonts): feed hb-view text via --text-file — C-locale containers reject non-ASCII argv

Arabic/RTL text through argv hit hb-view's 'Invalid byte sequence in
conversion input' under the POSIX locale (no LC_ALL in minimal images);
a temp file sidesteps locale conversion and option parsing alike.
Verified in-container: مرحبا shapes to 6 ligature outlines.