Rename apps/quickshell.lua to apps/omarchy-shell.lua and gather every
rule that targets a Quickshell surface owned by the shell:
- menu and image-selector layer rules (image-selector moved out of
apps/system.lua, where it didn't belong with generic floating /
media / idle rules)
- new window rules so the settings panel floats centered at 960x700
instead of tiling
The settings panel is a transient dialog, not a workspace surface, so
tiling it disrupts the layout and leaves it awkwardly tall when it lands
in a half-screen split. Class+title scoping keeps the rule from leaking
into other org.quickshell windows (menu, image picker, etc.).