Instructor analytics dashboard (distributions, struggle indicators)

[JimWallace]

Context

The admin dashboard has runner/health analytics. The instructor view has activity cards (v0.4.48) but nothing aggregating student performance across an assignment. Modern systems give you histograms, time-to-first-pass distributions, and "this test is failing for 70% of students — your spec is probably ambiguous" signals.

Goal

Per-assignment analytics page:

• Score distribution histogram (final / best-submission scores).
• Time-to-first-pass distribution (how long from first attempt → first all-green).
• Submissions-per-student distribution.
• Per-test pass-rate sorted descending — easy to spot outlier-hard tests.
• "Students with zero submissions" call-out.
• "Students whose last submission was >7 days ago and not passing" — at-risk indicator.

Per-course rollup:

• All assignments side-by-side: median score, % submitted, % passing.

Done when

• Instructor lands on a single dashboard URL per assignment showing the above.
• Loads in <1 s for a class of 300.
• Charts use the existing sparkline / chart stack from the admin dashboard.

Out of scope

• Statistical inference (item response theory, etc.) — descriptive only.
• Per-student deep-learning predictions.