feat: Dual-OS Neovim MCP Integration

- Created linux-nvim and win-nvim MCP servers for deep Neovim Msgpack-RPC integration.
- Implemented tools: nvim_goto_line, nvim_get_active_buffer, nvim_get_cursor, nvim_get_visual_selection, nvim_set_diagnostics.
- Added gemini-integration.lua for active UI socket discovery.
- Updated build.cmd to cross-compile for both Windows (gnu) and Linux (musl).
- Updated README, design.md, and instructions.md with architecture and tool capabilities.

README.md

@@ -82,3 +82,18 @@ You can also programmatically query these live metrics via the API endpoint:
 
 ## Further Reading
 For a deep dive into the architecture, Write-Ahead Logging (WAL), locking mechanisms, and the HTTP SSE event loop, consult the design.md file in this repository.
+
+## Neovim Integration
+The `linux-nvim` and `win-nvim` MCP servers provide direct Msgpack-RPC communication with Neovim.
+For this to work, you must add the provided `gemini-integration.lua` file to your Neovim `lua/` configuration directory and require it in your `init.lua`:
+```lua
+require('gemini-integration')
+```
+This script allows Neovim to broadcast its active socket to `~/.gemini/active_nvim.txt` when it gains focus, allowing the MCP servers to bridge the connection.
+
+These MCP servers provide the following two-way integration tools:
+*   **`nvim_goto_line`**: Open files and jump cursors directly from the LLM.
+*   **`nvim_set_diagnostics`**: Push inline code review warnings as virtual text.
+*   **`nvim_get_active_buffer`**: Read live, unsaved buffer contents.
+*   **`nvim_get_cursor`**: Fetch precise line/column coordinates.
+*   **`nvim_get_visual_selection`**: Read highlighted code blocks.