feat: refine sidebar UI and update download categories

- Restructured layout so the sidebar acts as an edge-to-edge curved layer with a shadow
- Replaced old download categories with Musics, Movies, Compressed, Documents, Pictures, Applications, and Other
- Updated Settings > Locations tab to handle the new categories
- Added extensive predefined file extensions for smart auto-categorization of downloads

test_regex.rs

@@ -0,0 +1,13 @@
+use regex::Regex;
+
+fn main() {
+    let pct_re = Regex::new(r"\[download\]\s+(\d+(?:\.\d+)?)%").unwrap();
+    let line = "[download]   0.0% of   15.59MiB at    7.28KiB/s ETA 36:34";
+    if line.contains("[download]") && line.contains("%") {
+        let fraction = pct_re.captures(&line)
+            .and_then(|cap| cap.get(1))
+            .and_then(|m| m.as_str().parse::<f64>().ok())
+            .unwrap_or(0.0) / 100.0;
+        println!("Fraction: {}", fraction);
+    }
+}