Match routed Vuforia 404 HTML responses - #3461

Closes #3396.

What

• Return the gzipped HTML Not Found response used by the Cloud Targets application for unrouted requests under /summary, /targets, and /duplicates.
• Keep the empty edge 404 for unrelated path prefixes.
• Include the request method/path and application response headers.
• Extend the cross-backend verified-fake tests and remove the resolved documented difference.

Checks

• Real Vuforia unrouted-path and unrouted-method cases
• Flask/Docker in-memory equivalents
• uv run --extra=dev prek run --files src/mock_vws/_flask_server/vws.py tests/mock_vws/test_invalid_given_id.py docs/source/differences-to-vws.rst