Commands for adjusting font size are changing my font size settings

[injust]

Summary

Steps to trigger the problem:

1. Configure the buffer_font_size setting
2. Use the zed::IncreaseBufferFontSize/DecreaseBufferFontSize/ResetBufferFontSize commands

Actual Behavior:

• cmd-plus/minus (zed::IncreaseBufferFontSize/DecreaseBufferFontSize) changes the buffer_font_size setting
• cmd-0 (zed::ResetBufferFontSize) sets "buffer_font_size": null, which uses the value of 15 from the default settings

Expected Behavior:

1. Set a font size in settings.json, which is the "default" font size
2. cmd-plus/minus (zed::IncreaseBufferFontSize/DecreaseBufferFontSize) to temporarily adjust the font size, without changing the buffer_font_size setting
3. cmd-0 (zed::ResetBufferFontSize) to reset to my configured default font size

Zed Version and System Specs

Zed: v0.171.6 (Zed)
OS: macOS 15.3.0
Memory: 16 GiB
Architecture: x86_64

[SomeoneToIgnore]

#23505