Extract the Flask/Docker implementation into a separate repository with shared contract tests #3737

The Flask/Docker implementation currently ships alongside the in-memory MockVWS implementation. Move the Flask apps and container deployment into a separate repository while keeping a single authoritative API contract test suite in vws-python-mock that both implementations can run.

The existing tests/mock_vws/fixtures/vuforia_backends.py already runs shared tests against in-memory, Flask-in-process, and real-Vuforia backends. However, it imports and configures all implementations together. Shared helpers also branch on concrete backend identities, and prepared-request helpers hardcode Vuforia URLs. Decouple these before extracting the server.

Proposed ownership:

• vws-python-mock: MockVWS, shared models, validators and API logic, core-specific tests, and the shared API contract test suite.
• New server repository (name to be decided): Flask VWS/VWQ apps, target-manager service, Dockerfiles/build configuration, container image releases, deployment documentation, and Flask/deployment-specific tests.
• The server depends on the core package at runtime. Expose a small supported interface for the shared functionality it needs instead of copying implementation logic or relying indefinitely on private core modules.

Make the shared contract tests a separately installable Python package maintained in the core repository, for example under contract-tests/, with a unique import namespace such as vws_mock_contract_tests. This is a development dependency of the server, not a runtime dependency. Initially it can be installed from a Git dependency pinned to a commit and subdirectory; a separate PyPI publication can follow if useful.

Load shared fixtures and each implementation's backend adapter explicitly as pytest plugins, and collect the installed test package with pytest --pyargs. Do not rely on the consuming repository's local conftest.py applying to tests installed elsewhere.

Acceptance criteria:

• Shared assertions execute unchanged against both implementations. Each repository owns its backend adapter and setup/cleanup behavior; the shared suite does not import Flask or the server package.
• Backend fixtures provide API clients/endpoint URLs, database setup/reset, and mock controls such as database creation and recognition-count seeding. Shared helpers call these operations rather than branching on concrete backend identities.
• Endpoint URLs are configurable so the suite can exercise actual server deployments as well as in-process mocks.
• Mock-only tests use synthetic credentials and do not require real-Vuforia secrets. Retain explicit real-Vuforia verification and its existing account/capability restrictions.
• Core interception tests stay in core. Flask routing, concurrency, health checks, container restart/state-persistence tests, and image build tests move with the server. Shared API tests include their required fixtures, helpers, and test assets in the installable package.
• Server CI runs the shared suite against Flask in-process and applicable cases against the actual three-service deployment. Preserve and document transport-specific limitations, including malformed Content-Length behavior; the in-process adapter does not prove deployed behavior.
• Pin the server's core dependency and contract suite to compatible revisions and update them through normal PRs. Add a scheduled compatibility run against core main to detect upcoming changes.
• Both repositories retain meaningful coverage gates for the code they own, with CI partitions, packaging checks, documentation, and release workflows updated for the split.
• Preserve or provide a documented migration for published image names, image targets, environment variables, and deployment instructions.

Suggested sequence: first decouple and package the contract suite while both implementations remain in this repository; verify both adapters; then extract Flask/Docker and validate the new repository against the same suite.

Related: #3724 concerns a separate deployment launcher that consumes published images. This issue concerns ownership of the Flask implementation, images, and reusable tests.

Implementation breakdown:

• Decouple shared API tests from concrete mock implementations #3738: Decouple shared API tests from concrete mock implementations.
• Package the shared API contract suite for reuse from another repository #3739: Package the shared API contract suite for reuse from another repository.
• Expose a supported core interface for the Flask server #3740: Expose a supported core interface for the Flask server.
• Extract Flask apps and Docker deployment into a separate server repository #3741: Extract Flask apps and Docker deployment into a separate server repository.

Order: #3738 before #3739; #3740 can proceed independently; #3741 is blocked by #3739 and #3740.