zsh $VAR:text in ffmpeg filters silently becomes basename modifier

In zsh scripts, drawtext=fontfile=$FONT:text=... expands $FONT:t as the history-style tail modifier (basename) and swallows the :text= key, causing the misleading ffmpeg error: Either text, a valid file, a timecode or text source must be provided. Fix: always brace-expand ${FONT}:text=. Related gotchas in the same build: drawtext fails to parse .ttc font collections (use a .ttf like Supplemental/Arial.ttf), sandboxed shells can mangle nested single quotes inside double-quoted -vf strings (avoid inner quotes, no commas in values), and ffmpeg tile filter needs uniform input dimensions or it emits partial/black sheets.