feat: Bessere Erkennung von Doppel-Extensions

- .tar.gz, .tar.bz2, .tar.xz, .tar.zst, .tar.lz, .tar.Z
  werden jetzt korrekt als Einheit behandelt
- "my archive.tar.gz" → "my_archive.tar.gz" (nicht mehr "my_archive.gz")
- Neue Hilfsfunktion split_filename()
- Tests für Doppel-Extensions hinzugefügt

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/sanitizer.rs

@@ -13,6 +13,38 @@ static RE_INVALID: Lazy<Regex> = Lazy::new(|| Regex::new(r"[^\w.\-]").unwrap());
 static RE_ADJACENT: Lazy<Regex> = Lazy::new(|| Regex::new(r"_\.|\._").unwrap());
 static RE_MULTI: Lazy<Regex> = Lazy::new(|| Regex::new(r"[_\.]{2,}").unwrap());
 
+// Bekannte Doppel-Extensions (z.B. .tar.gz)
+const DOUBLE_EXTENSIONS: &[&str] = &[
+    ".tar.gz",
+    ".tar.bz2",
+    ".tar.xz",
+    ".tar.zst",
+    ".tar.lz",
+    ".tar.Z",
+];
+
+/// Trennt Dateiname in Basis und Extension, berücksichtigt Doppel-Extensions
+fn split_filename(filename: &str) -> (String, String) {
+    // Prüfe auf bekannte Doppel-Extensions
+    for double_ext in DOUBLE_EXTENSIONS {
+        if filename.ends_with(double_ext) {
+            let base_len = filename.len() - double_ext.len();
+            if base_len > 0 {
+                return (
+                    filename[..base_len].to_string(),
+                    double_ext.to_string(),
+                );
+            }
+        }
+    }
+
+    // Standard-Fall: nur letzte Extension
+    match filename.rsplit_once('.') {
+        Some((b, e)) if !b.is_empty() => (b.to_string(), format!(".{e}")),
+        _ => (filename.to_string(), String::new()),
+    }
+}
+
 /// Bereinigt den übergebenen Dateinamen oder Verzeichnisnamen.
 pub fn clean_filename(name: &OsStr, config: &Config, verbose: bool) -> Option<String> {
     let original = name.to_string_lossy();
@@ -24,10 +56,7 @@ pub fn clean_filename(name: &OsStr, config: &Config, verbose: bool) -> Option<St
     };
 
     // Stamm und Extension trennen (nur im Rest, nicht im hidden_prefix)
-    let (mut base, mut ext) = match rest.rsplit_once('.') {
-        Some((b, e)) if !b.is_empty() => (b.to_string(), format!(".{e}")),
-        _ => (rest.to_string(), String::new()),
-    };
+    let (mut base, mut ext) = split_filename(rest);
 
     // Platzhalter (C++, c++, C#, c#) anlegen
     base = preserve_special_identifiers(&base);
@@ -290,19 +319,56 @@ mod tests {
             Some("test_file.txt".to_string())
         );
 
-        // Double extension (currently only keeps last)
+        // Double extension with spaces in base name
         assert_eq!(
-            clean_filename(OsStr::new("archive.tar.gz"), &config, false),
-            None // No special chars to clean
+            clean_filename(OsStr::new("my archive.tar.gz"), &config, false),
+            Some("my_archive.tar.gz".to_string())
         );
 
-        // Multiple dots
+        // Other double extensions
+        assert_eq!(
+            clean_filename(OsStr::new("backup file.tar.bz2"), &config, false),
+            Some("backup_file.tar.bz2".to_string())
+        );
+
+        assert_eq!(
+            clean_filename(OsStr::new("data set.tar.xz"), &config, false),
+            Some("data_set.tar.xz".to_string())
+        );
+
+        // Multiple dots (not a double extension)
         assert_eq!(
             clean_filename(OsStr::new("foo..bar.txt"), &config, false),
             Some("foo.bar.txt".to_string())
         );
     }
 
+    #[test]
+    fn test_split_filename() {
+        // Double extensions
+        assert_eq!(
+            split_filename("archive.tar.gz"),
+            ("archive".to_string(), ".tar.gz".to_string())
+        );
+
+        assert_eq!(
+            split_filename("backup.tar.bz2"),
+            ("backup".to_string(), ".tar.bz2".to_string())
+        );
+
+        // Single extension
+        assert_eq!(
+            split_filename("file.txt"),
+            ("file".to_string(), ".txt".to_string())
+        );
+
+        // No extension
+        assert_eq!(
+            split_filename("README"),
+            ("README".to_string(), String::new())
+        );
+    }
+
     #[test]
     fn test_clean_filename_special_identifiers() {
         let config = Config::default();