feat: implement fuzzy search and replace functionality with Levenshtein distance

- Added `applySearchReplace` function to handle search and replace operations with fuzzy matching capabilities.
- Introduced tests for various scenarios including fuzzy matching with typos, exact matches, and handling whitespace differences.
- Created a parser for search/replace blocks to facilitate the new functionality.
- Updated prompts for search-replace operations to clarify usage and examples.
- Added utility functions for text normalization and language detection based on file extensions.
- Implemented a minimal stdio MCP server for local testing with tools for adding numbers and printing environment variables.

AGENTS.md

@@ -0,0 +1,30 @@
+# Repository Agent Guide
+
+## Project context
+
+- This is an Electron application with a secure IPC boundary.
+- Frontend is a React app that uses TanStack Router (not Next.js or React Router).
+- Data fetching/mutations should be handled with TanStack Query when touching IPC-backed endpoints.
+
+## IPC architecture expectations
+
+1. `src/ipc/ipc_client.ts` runs in the renderer. Access it via `IpcClient.getInstance()` and expose dedicated methods per IPC channel.
+2. `src/preload.ts` defines the renderer allowlist. New IPC APIs must be added here.
+3. `src/ipc/ipc_host.ts` registers handlers that live in files under `src/ipc/handlers/` (e.g., `app_handlers.ts`, `chat_stream_handlers.ts`, `settings_handlers.ts`).
+4. IPC handlers should `throw new Error("...")` on failure instead of returning `{ success: false }` style payloads.
+
+## React + IPC integration pattern
+
+When creating hooks/components that call IPC handlers:
+
+- Wrap reads in `useQuery`, providing a stable `queryKey`, async `queryFn` that calls the relevant `IpcClient` method, and conditionally use `enabled`/`initialData`/`meta` as needed.
+- Wrap writes in `useMutation`; validate inputs locally, call the IPC client, and invalidate related queries on success. Use shared utilities (e.g., toast helpers) in `onError`.
+- Synchronize TanStack Query data with any global state (like Jotai atoms) via `useEffect` only if required.
+
+## General guidance
+
+- Favor descriptive module/function names that mirror IPC channel semantics.
+- Keep Electron security practices in mind (no `remote`, validate/lock by `appId` when mutating shared resources).
+- Add tests in the same folder tree when touching renderer components.
+
+Use these guidelines whenever you work within this repository.