Tutorial v2: Frontend Tutorial project business models

[nighca]

Parent

Part of #3403.

Background

Playground Course content crosses the Course API boundary as an opaque FileCollection. The frontend needs a typed Tutorial-project business model, analogous to the existing SPX models in spx-gui/src/models/spx/, to own the Course project format and safely turn it into the in-memory representations used by authoring, preview and learning.

Scope

• Add frontend Tutorial-project domain models under spx-gui/src/models/ following the conventions used by spx-gui/src/models/spx/.
• Define the typed representation and validation/loading/serialization boundary for the Tutorial-project file collection: Course metadata, embedded SPX project files, Tutorial program and course-local assets.
• Keep the persisted/API representation as FileCollection; interpret it into the typed model only in the frontend.
• Provide the model operations needed to construct an ownerless in-memory SpxProject, clone project state for preview/learning, and serialize updated Course content without leaking mutable author state.
• Add focused tests for valid and invalid Tutorial-project file collections and for clone/round-trip behavior.

Design references

• Tutorial v2 overview: Course APIs and Course playground
• Course API contract
• SPX Project Editor contract
• Course Editor contract

Acceptance criteria

• The model has a single documented mapping between the opaque FileCollection and the typed Tutorial-project representation.
• Invalid or incomplete Course content is reported as a model/load error rather than reaching editor or Tutorial runtime code as unchecked paths.
• Loading, editing, cloning and serializing do not share mutable project/file state between the author, preview and learner sessions.
• The model creates an in-memory SPX project without owner or cloud-project identity, preserving the existing effect-free editor behavior.

Dependencies

• Tutorial v2: Tutorial lifecycle and Course playground #3419 (Tutorial lifecycle and Course playground) depends on this model to load the Course project and build its session-local editor project.
• Tutorial v2: Course Editor and preview #3420 (Course Editor and preview) depends on this model to edit typed Tutorial-project content and create isolated preview snapshots.

Development coordination

Follow the coordination requirements in #3403:

• Create the implementation branch from the latest goplus/issue-3403-tutorial-v2 and target that integration branch in the pull request until the initiative is integrated into dev.
• Follow the User Tutorial v2 product design and the relevant contracts in the Tutorial v2 tech design.
• If this work changes a shared decision or module contract, update the corresponding design document in the same child PR rather than silently diverging from it.