Migrate server.py to the mcp 2.0 Server API (currently pinned to mcp<2.0.0) #20

Follow-up to #16 / #18.

Background

mcp 2.0.0 removed the 1.x decorator API on Server (@app.list_tools(), @app.call_tool(), @app.list_resources(), @app.read_resource()), which src/finmind_mcp/server.py is written against. We shipped 0.0.6 with mcp>=1.0.0,<2.0.0 as immediate stopgap so installs stop crashing — but that pin is a ceiling, not a fix.

Why this matters

• mcp 1.x will stop getting fixes at some point; we're frozen out of 2.x features and security updates.
• Users with another MCP package in the same environment that requires mcp>=2.0 now hit an unsolvable resolver conflict.

Scope

• Port the four decorator registrations in src/finmind_mcp/server.py to the 2.0 API (evaluate whether the FastMCP-style API is the better target while we're in there).
• Check stdio_server / mcp.types imports for renames.
• Bump the floor to mcp>=2.0.0 (or keep a compat shim if we want to support both) and drop the upper pin.
• Re-run the smoke test + regression runner against a real MCP host (Claude Desktop / Claude Code) — unit tests alone won't catch a protocol-level regression.

Notes

Whether to support mcp 1.x and 2.x simultaneously is worth deciding up front — a single-version jump is much less code, but breaks anyone stuck on 1.x.