fix: gate init_in_memory as test-only to resolve clippy dead_code warning

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/src/db.rs

@@ -10,6 +10,7 @@ pub fn init(db_path: &Path) -> Result<Connection> {
     Ok(conn)
 }
 
+#[cfg(test)]
 pub fn init_in_memory() -> Result<Connection> {
     let conn = Connection::open_in_memory()?;
     configure(&conn)?;