Fix#2301 Remove unused Look & Feel font options

[leehaut]

Fix #2301

Summary

• Remove the Default font and Note font pickers from Look & Feel. Default UI text already follows the OS system font (plus Global Zoom), so the Default font setting had no effect.
• Keep Fixed width font (SQL, scripts, logs) and Font on workspace (canvas labels). Notes without a per-note font now fall back to the workspace font.
• Ignore leftover FontDefault* / FontNote* keys in existing hop-config.json files; they are no longer read or written.