fix: address audit findings — security, performance, and correctness

- Use absolute paths for all binaries in power.rs to prevent PATH hijacking
- Implement POWER_TIMEOUT via try_wait() polling (was declared but unused)
- Fix potential panic in load_background_texture when GResource path
  fails to_str() — now falls back to known wallpaper resource path
- Compress wallpaper.jpg in GResource bundle (saves ~374 KB in binary)
- Merge double idle_add_local_once into single cycle for faster focus
- Centralize GRESOURCE_PREFIX as pub(crate) const in main.rs
- Fix fallback user UID from 0 (root) to u32::MAX
- Fix CSS comment: "square card" → "circular card" (border-radius: 50%)

src/main.rs

@@ -12,9 +12,11 @@ use gtk4::prelude::*;
 use gtk4::{self as gtk, gio};
 use gtk4_layer_shell::LayerShell;
 
+pub(crate) const GRESOURCE_PREFIX: &str = "/dev/moonarch/moonset";
+
 fn load_css(display: &gdk::Display) {
     let css_provider = gtk::CssProvider::new();
-    css_provider.load_from_resource("/dev/moonarch/moonset/style.css");
+    css_provider.load_from_resource(&format!("{GRESOURCE_PREFIX}/style.css"));
     gtk::style_context_add_provider_for_display(
         display,
         &css_provider,