fix(introspect): treat Windows drive letters as bare paths, not URL schemes

`C:\path\to\db.sqlite` parses as a URL with scheme `c`, which routed the
input to the UnsupportedScheme branch and broke the SQLite roundtrip
test on the Windows CI runner. A single-letter "scheme" is almost
always a Windows drive letter, so short-circuit URL parsing for that
case and let the input fall through as a filesystem path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: davidsmfreire

sqlshield-introspect/src/lib.rs

@@ -54,6 +54,14 @@ pub fn introspect(db_url: &str) -> Result<TablesAndColumns, IntrospectError> {
 }
 
 fn url_scheme(s: &str) -> Option<String> {
+    // Windows drive letters (`C:\…`) parse as a single-character URL
+    // scheme, which would otherwise route a bare path through the
+    // unsupported-scheme branch. Treat any single-letter "scheme" as a
+    // bare filesystem path.
+    let bytes = s.as_bytes();
+    if bytes.len() >= 2 && bytes[1] == b':' && bytes[0].is_ascii_alphabetic() {
+        return None;
+    }
     url::Url::parse(s)
         .ok()
         .map(|u| u.scheme().to_ascii_lowercase())
@@ -170,4 +178,12 @@ mod tests {
         assert!(tables["users"].contains("name"));
         assert!(tables["orders"].contains("user_id"));
     }
+
+    #[test]
+    fn windows_drive_letter_is_not_treated_as_url_scheme() {
+        assert_eq!(url_scheme("C:\\foo\\bar.db"), None);
+        assert_eq!(url_scheme("d:/relative.sqlite"), None);
+        assert_eq!(url_scheme("postgres://x/y").as_deref(), Some("postgres"));
+        assert_eq!(url_scheme("/abs/path.db"), None);
+    }
 }