Backend: Create Remove Saved Project Endpoint

[Vriti62]

Description
This sub-issue covers the backend implementation for removing a project from an existing saved collection.
Users should be able to delete/un-save a project they had previously added to their collection.

Tasks / Requirements
-Create an authenticated DELETE endpoint to remove a project from a user’s saved collection.
-Validate that the project exists in the collection before attempting removal.
-Return the updated collection after removal.

refers: #1180

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[Avdhesh-Varshney]

@Vriti62 Also add a middleware to verify the user before remove project from the collection