Add comprehensive VuMark instance generation tests

[adamtheturtle]

Summary

• Add parametrized tests for PNG, SVG, and PDF output formats
• Add tests for invalid Accept header (returns InvalidAcceptHeader 400) and empty instance_id (returns InvalidInstanceId 422)
• Organise VuMark tests into a class with verify_mock_vuforia applied at class level
• Implement Accept header validation and correct multi-format responses in both mock backends
• Add INVALID_ACCEPT_HEADER and INVALID_INSTANCE_ID to ResultCodes enum with corresponding exception classes
• Add minimal SVG and PDF mock response content alongside the existing PNG
• Document VuMark image simplification (fixed minimal image, instance_id not encoded) in differences-to-vws.rst

Test plan

• All new tests verified against real Vuforia before implementing mock support (TDD)
• All 15 VuMark tests pass on all three backends (Real Vuforia, In Memory Mock, Docker In Memory)
• All pre-commit hooks pass (ruff, mypy, pyright, vulture, etc.)

🤖 Generated with Claude Code

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Note

Medium Risk
Changes the mock VuMark instance endpoint behavior (Accept negotiation and required instance_id), which may break consumers relying on the previous always-PNG/lenient behavior; impact is limited to the mock/test backends.

Overview
Adds content negotiation to VuMark instance generation so /targets/{id}/instances can return image/png, image/svg+xml, or application/pdf based on the Accept header in both the Flask and requests-mock backends.

Introduces new ResultCodes/ValidatorErrors for InvalidAcceptHeader (400) and InvalidInstanceId (422), plus minimal SVG/PDF mock payloads, and expands the test suite to cover format selection and these error cases.

Updates the Docker build GitHub Action to explicitly pass docker-bake.hcl to the bake check/build steps.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Case-insensitive header lookup lost by dict conversion

Low Severity

dict(request.headers).get("Accept", "") converts the CaseInsensitiveDict from PreparedRequest.headers into a plain dict, losing case-insensitive lookup. This means a header sent as e.g. accept: image/png won't be found, incorrectly triggering InvalidAcceptHeaderError. The Flask backend at the equivalent point uses request.headers.get(key="Accept", default="") which preserves case-insensitive behavior, creating an inconsistency between the two mock backends.