feat(06-01): add --cookies and --cookies-from-browser CLI args

- Add --cookies <FILE> for Netscape-format cookie files
- Add --cookies-from-browser <BROWSER> for browser cookie extraction
- Add CLI tests for both arguments
- 140 tests pass

src/cli.rs

@@ -122,6 +122,17 @@ pub struct Args {
     /// Shorthand for --download-archive with default path
     #[arg(long = "download-archive-skip-duplicates")]
     pub download_archive_skip_duplicates: bool,
+
+    // ===== Authentication Options =====
+    /// Path to Netscape-format cookies file
+    /// Use browser extensions like "Get cookies.txt LOCALLY" to export cookies
+    #[arg(long = "cookies", value_name = "FILE")]
+    pub cookies: Option<PathBuf>,
+
+    /// Extract cookies from browser (firefox, chrome, edge, etc.)
+    /// Requires browser-cookie3 library or similar to be installed
+    #[arg(long = "cookies-from-browser", value_name = "BROWSER")]
+    pub cookies_from_browser: Option<String>,
 }
 
 impl Args {
@@ -340,4 +351,43 @@ mod tests {
         assert_eq!(config.command, "scan");
         assert_eq!(config.args, vec!["{}", "--verbose"]);
     }
+
+    #[test]
+    fn test_cookies_arg() {
+        let args = Args::parse_from([
+            "gallery-dl",
+            "--cookies",
+            "cookies.txt",
+            "https://example.com",
+        ]);
+        assert_eq!(args.cookies, Some(PathBuf::from("cookies.txt")));
+        assert_eq!(args.urls.len(), 1);
+        assert_eq!(args.urls[0], "https://example.com");
+    }
+
+    #[test]
+    fn test_cookies_from_browser_arg() {
+        let args = Args::parse_from([
+            "gallery-dl",
+            "--cookies-from-browser",
+            "firefox",
+            "https://twitter.com/user",
+        ]);
+        assert_eq!(args.cookies_from_browser, Some("firefox".to_string()));
+        assert_eq!(args.urls.len(), 1);
+    }
+
+    #[test]
+    fn test_cookies_args_combined() {
+        let args = Args::parse_from([
+            "gallery-dl",
+            "--cookies",
+            "cookies.txt",
+            "--cookies-from-browser",
+            "chrome",
+            "https://example.com",
+        ]);
+        assert_eq!(args.cookies, Some(PathBuf::from("cookies.txt")));
+        assert_eq!(args.cookies_from_browser, Some("chrome".to_string()));
+    }
 }