getProgressByLearner silently ignores limit/offset when courseId absent

[DeFiVC]

What

When courseId is undefined (the "all courses" path), the function executes a DISTINCT ON (course_id) query that returns all courses for the learner without applying LIMIT or OFFSET. The pagination parameters are silently discarded.

Why

A learner with hundreds of courses would return all records in a single response, causing large payloads and potential memory/performance issues. The API at routes.ts:100-105 passes limit and offset through to this function, giving callers the false impression pagination is supported.

Scope

• Apply limit and offset to the DISTINCT ON query
• Or document that pagination is not supported for this path

Acceptance Criteria

• Pagination is applied consistently
• Or documentation reflects the actual behavior

Technical Context

• File: src/database/queries.ts, lines 164-172