feat: add FetchUrlTool with proxy support and cross-OS path sanitization

- Implement native FetchUrlTool using reqwest for HTTP fetching, which respects HTTP_PROXY, HTTPS_PROXY, and NO_PROXY natively.
- Introduce sanitize_path in utils to bidirectionally handle Windows/WSL path mapping, applying it to various search/git handlers.
- Update .gitignore to exclude mcp_store.redb and tantivy_index.

server/src/handlers/ast.rs

@@ -440,7 +440,7 @@ fn scan_workspace_for_symbol(
 
                         if is_match {
                             results.push(serde_json::json!({
-                                "file_path": path.to_string_lossy(),
+                                "file_path": crate::handlers::utils::sanitize_path(&path.to_string_lossy()),
                                 "line": line_num + 1,
                                 "content": line.trim(),
                             }));