Seed preview projects for local/preview work

[DNR500]

Arises from issue: 1653

Summary

Adds unowned Blocks (code_editor_scratch) templates to test seeds so Experience CS project previews can be loaded from editor-api without auth (and without waiting on ExCS content sync).
Pairs with the classroom preview route work in editor-standalone - see this editor-standalone PR.

• Seed excs-preview-starter as a public Scratch template (user_id / school_id nil) with real Scratch JSON and instruction steps
• Also seed the same identifier in fr-FR with a French name and instructions, so locale-aware ProjectLoader requests return translated project content instead of falling back to English
• Wire create/destroy into test_seeds:create / test_seeds:destroy (and thus /test/reseed)
• Cover create, destroy, idempotent instruction updates, and the French locale row in spec/lib/test_seeds_spec.rb

Why

#1653 needs a stable public Blocks project that classroom can open at a preview URL while logged out. Production templates will come from ExCS sync later; this seed unblocks local and PR testing.

How to try it

docker compose exec api bundle exec rake test_seeds:create
# or
curl -X POST http://localhost:3009/test/reseed -H "X-RESEED-API-KEY: $RESEED_API_KEY"

curl -s 'http://localhost:3009/api/projects/excs-preview-starter?locale=en' | head
curl -s 'http://localhost:3009/api/projects/excs-preview-starter?locale=fr-FR' | head
curl -s 'http://localhost:3009/api/scratch/projects/excs-preview-starter' | head

English and French project metadata should differ; Scratch content is shared.

Note: if the API process has been up a long time, restart it (or run rake test_seeds:create in a fresh docker compose exec) so reseed picks up the new rake task code.

[github-actions]

Test coverage

92.3% line coverage reported by SimpleCov.
Run: https://github.com/RaspberryPiFoundation/editor-api/actions/runs/31731838748

[Copilot]

Pull request overview

Adds a public (unowned) Scratch/Blocks “preview starter” template into the test seeding flow so classroom preview routes can load a stable project from editor-api without authentication, including a French locale variant to validate locale-aware loading.

Changes:

• Introduces ProjectPreviewSeedsHelper to upsert/destroy an unowned code_editor_scratch template (excs-preview-starter) with seeded Scratch JSON and instruction steps (EN + FR).
• Wires preview project create/destroy into test_seeds:create and test_seeds:destroy.
• Extends spec/lib/test_seeds_spec.rb to cover creation, destruction, and instruction updates, including the fr-FR row.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
spec/lib/test_seeds_spec.rb	Adds specs asserting the preview template is created (EN/FR), updated, and removed via test seed tasks.
lib/tasks/test_seeds.rake	Hooks preview template lifecycle into the test reseed rake tasks.
lib/tasks/seeds_helper.rb	Pulls preview seeding helpers/constants into the existing seeding helper module.
lib/tasks/project_preview_seeds_helper.rb	Implements upsert/destroy logic for the public Scratch preview template and reads seed JSON from disk.
lib/tasks/seed_data/excs_preview_starter.json	Adds seeded Scratch project JSON payload for the preview template.
lib/tasks/seed_data/excs_preview_starter_instructions.json	Adds English instruction steps for the preview template.
lib/tasks/seed_data/excs_preview_starter_instructions_fr.json	Adds French instruction steps for the preview template.

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