fix: map FastApiMCP description to instructions, not version

[Amiirhosseini]

Summary

• Stops passing description as the second positional arg to mcp.server.Server (on mcp>=1.12 that field is version, which is why MCP Inspector showed the description under Version).
• Passes version=self.fastapi.version and maps the human description to instructions (and description when the installed SDK exposes that keyword).
• Adds a regression test.

Fixes #293
Fixes #322

Test plan

• pytest tests/test_configuration.py::test_description_is_not_passed_as_mcp_version passes on mcp 1.30
• Confirmed server.version == FastAPI.version and server.instructions == description

[Copilot]

🟢 Approval recommended

The change directly addresses the reported MCP signature mismatch and includes a targeted regression test covering the corrected mapping behavior.

Pull request overview

This PR fixes compatibility with mcp>=1.12 by avoiding passing FastApiMCP.description as a positional argument to mcp.server.lowlevel.server.Server, where it would bind to version, and instead mapping the human-readable description to instructions (and description when supported) while setting the MCP server version from the FastAPI app version.

Changes:

• Update FastApiMCP.setup_server() to construct Server(...) using keyword arguments (version, instructions, and optionally description) based on the installed MCP SDK signature.
• Add a regression test ensuring description does not bind to Server.version and that Server.instructions receives the description.

File summaries

File	Description
fastapi_mcp/server.py	Switches MCP Server construction to keyword args and maps FastAPI version + human description correctly across MCP SDK versions.
tests/test_configuration.py	Adds a regression test validating the corrected Server.version and Server.instructions mappings.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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