refactor: extract constants, deduplicate defaults, improve config loading

- Define NUM_COMMANDS and DEFAULT_COMMANDS to eliminate repeated arrays
- Initialize commands to NULL and fall back to defaults on config read errors
- Skip empty lines and handle malformed entries gracefully in load_configuration
- Show a "Configuration saved." toast on successful settings save
- Fix window parent lookup via gtk_application_get_active_window

.gitignore

@@ -1,3 +1,7 @@
 ssdd
 resources.c
 resources.h
+
+# ZaguanBlade local data
+.zblade/
+.pnpm-store/