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/router.rs

@@ -536,6 +536,7 @@ impl MemoryHandler {
         register!(graph::SummarizeSubgraphHandler);
         register!(meta::AgentSignalsHandler);
         register!(meta::AutoSessionCheckpointHandler);
+        register!(http::FetchUrlHandler);
 
         Self {
             state,