Fix monospace font preference ordering

[derluke]

Summary

• keep JetBrainsMono as the packaged monospace default while leaving the generic family in the pattern for a later user override
• scope both default and selected-font rules to requests where monospace is the first family, preserving explicit application fonts
• migrate only the exact Fontconfig file generated by the previous omarchy font set implementation

Why

The package rule currently assigns JetBrainsMono before 50-user.conf loads. That removes monospace from the pattern, so the selected-font rule never matches. Appending the packaged default keeps the generic family available for the user rule; qualifying the first family prevents a recurrence of the app-specific font override fixed in #5700.

Testing

• bash test/shell.d/fontconfig-test.sh
• ./test/cli