gpf_wfs_get_feature_by_id

[esgn]

closes #48

Summary

This PR introduces a new MCP tool, gpf_wfs_get_feature_by_id, to reliably fetch a single WFS feature by its exact identifier and avoid ambiguous same-layer spatial intersections.

What changed

• Added gpf_wfs_get_feature_by_id:
  • Input: typename, feature_id, optional select, result_type: results | request (hits intentionally not supported).
  • Strict cardinality checks:
    • 0 result => explicit error
    • >1 result => explicit error
    • returned ID mismatch => explicit error
• Added WFS request builder for by-id calls in wfs_internal/request.ts.
• Refactored shared response handling:
  • introduced attachFeatureRefs(...) in wfs_internal/response.ts.
• Reused existing property validation logic by exporting compileSelectProperty(...) from wfs_internal/compile.ts.
• Updated gpf_wfs_get_features:
  • rejects intersects_feature when typename === intersects_feature_typename
  • returns a guided error pointing to gpf_wfs_get_feature_by_id.
• Updated tool descriptions (adminexpress, cadastre, urbanisme, assiette_sup, gpf_wfs_get_features) to strongly direct exact feature_ref reuse to gpf_wfs_get_feature_by_id.
• Updated README documentation for the new workflow.

Tests

• Added dedicated test suite for gpf_wfs_get_feature_by_id.
• Extended strict input tests to include the new tool.
• Updated gpf_wfs_get_features tests to cover the new same-layer intersection guard and guidance behavior.

Validation

• npm run build passes (tool definitions validated).
• npm test passes (all suites green).