[CHORE]: Python server template — bump mcp to >=2,<3 and align minimum with live servers

[jonpspri]

Summary

After the template has been moved to this repository (tracked in #31), update the Python cookiecutter template's default pyproject.toml to target MCP SDK v2 and align its minimum version constraint with the live servers.

Changes required

1. MCP SDK version bump

# Before
mcp>=1.0.0,<2

# After
mcp>=2,<3

The current lower bound (1.0.0) is significantly behind what the live servers use (1.28.1). The bump to >=2,<3 brings the template in line with current practice and eliminates the drift.

2. Dev dependency alignment (optional)

Consider aligning the template's dev dependency pins (pytest, ruff, mypy, black) with the versions used in the live servers, so generated projects start from a current baseline.

3. Template documentation

Update the template README and any scaffold generation instructions to reflect the MCP SDK v2 API — particularly the MCPServer class name and any changed import paths.

Acceptance criteria

• mcp constraint updated to >=2,<3 in template pyproject.toml
• Generated project uses SDK v2 API patterns
• Template README reflects v2 usage
• CI green

References

• Depends on: [CHORE]: Move graphviz_server to mcp-servers/python/graphviz_server #31 (move issue)
• MCP SDK v2 migration epic: CF 1.x (x>0) - Support for MCP 2026-07-28 dual-era communication in ContextForge Gateway mcp-context-forge#6218
• Step 10 (mcp-servers update): [CHORE]: MCP SDK v2 — Update mcp-servers subpackages: FastMCP rename, dependency pins (Step 10/11) mcp-context-forge#6228