Support Nano, Micro, and Fresh as default editors

[CptPanko]

Summary

• accept nano, micro, and fresh in the default-editor setter
• install Nano and Micro from the repository and Fresh from fresh-editor-bin
• verify the selected executable exists before writing state or sending a success notification
• keep terminal and inline launcher behavior covered for all three editors

Testing

• bash test/shell.d/default-apps-test.sh (13 assertions, macOS and Ubuntu 24.04)
• planted installer-postcondition and empty-glyph mutations both fail the focused suite
• bin/omarchy commands --check under modern Bash
• parser-aware syntax checks for every bin/omarchy-* command
• git diff --check

./test/all was bounded at the existing sleep-lock-test.sh hang on macOS; the observed failures were unrelated host/tooling gaps, while the changed focused suite passed.

Fixes #316