refactor: extract noctalia settings to JSON
- Split 553-line noctalia.nix into noctalia/default.nix (56 lines) + noctalia/settings.json (497 lines)
- Nix-dependent config (lib.getExe, keybinds, qt) stays in default.nix
- Pure data settings loaded via lib.importJSON
- Update wm/default.nix import from ./noctalia.nix to ./noctalia