Add project favorites: database table and API endpoints

[JohnRDOrazio]

Context

Users should be able to favorite projects. This requires a new database table and API endpoints.

Database

New project_favorites table:

Column	Type	Description
user_id	text	FK to user (from auth provider)
project_id	UUID	FK to projects.id
created_at	timestamp	When favorited
PK	(user_id, project_id)	Composite primary key

API endpoints

• POST /api/v1/projects/{projectId}/favorite — add to favorites (idempotent)
• DELETE /api/v1/projects/{projectId}/favorite — remove from favorites
• GET /api/v1/projects — include is_favorited: boolean in each project response item (for authenticated users)

Sorting

When returning project lists, favorited projects should sort to the top (within the existing sort order). Consider adding a sort query parameter or always sorting favorites first for authenticated users.

Related

• Add project favorites with star icon and sort-to-top ontokit-web#78 — frontend: star icon and sort-to-top