Agent Skills: macos-font-defaults

Set macOS's "user fixed-pitch font" and per-app fixed-width fonts (TextEdit plain text, Stickies default note) to a chosen font — by default JetBrains Mono NL Nerd Font. Idempotent and parameterized, so it doubles as a fresh-machine setup step. Use when the operator wants their default monospaced/fixed-width font changed, or asks "make my fixed-width font X", "default mono font", "set Stickies/TextEdit font". TRIGGERS - default fixed-width font, monospaced font default, set my mono font, fixed-pitch font, Stickies default font, TextEdit plain text font.