Update AGENTS with repo overview

AGENTS.md

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+# AGENTS
+
+This repository contains the FastMCP source code and documentation.
+It is organized as follows:
+
+- `src/fastmcp/` – the main library implementation. Key modules include:
+  - `server/` with the `FastMCP` server and supporting classes like `Context`.
+  - `client/` with the high-level `Client` for connecting to MCP servers.
+  - subpackages for `resources`, `prompts`, `tools`, and other utilities.
+- `tests/` – pytest-based unit tests for the library.
+- `docs/` – documentation written for Mintlify and published on gofastmcp.com.
+- `examples/` – small example applications demonstrating library usage.
+
+Before committing any changes, run:
+
+```bash
+uv sync           # install dependencies
+uv run pre-commit run --all-files
+uv run pytest
+```
+
+`pre-commit` runs Ruff, Prettier, and Pyright. Make sure changes under
+`src/` or `tests/` include corresponding tests. Please keep this file
+updated if the repository layout or tooling changes.