Update Python requirement to 3.10+ for MCP compatibility

The MCP package requires Python 3.10 or higher. Updated:
- GitHub Actions workflow to test Python 3.10, 3.11, 3.12
- README.md badge to Python 3.10+
- CLAUDE.md prerequisites
- CONTRIBUTING.md prerequisites
- docs/MCP_SETUP.md prerequisites

This fixes the MCP installation error in CI:
'ERROR: No matching distribution found for mcp>=1.0.0'

MCP package versions 0.9.1+ all require Python 3.10+.

.github/workflows/tests.yml

@@ -13,11 +13,9 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest]
-        python-version: ['3.9', '3.10', '3.11', '3.12']
+        python-version: ['3.10', '3.11', '3.12']
         exclude:
           # Exclude some combinations to speed up CI
-          - os: macos-latest
-            python-version: '3.9'
           - os: macos-latest
             python-version: '3.10'