Track per-topic study progress / mastery

[nazim117]

Problem

There's no notion of "how well do I know X." Projects currently map to PM projects, not study subjects, and nothing tracks review history or confidence per concept.

Proposal

Once flashcards (#61) and/or concept extraction (#63) exist, add a lightweight mastery signal per concept/card: last reviewed, streak of correct recalls, a simple confidence score. Surface it as a per-project (or per-topic, if projects get reframed as subjects/courses) dashboard: what's solid, what's shaky, what hasn't been reviewed recently.

Depends on

• Add flashcards + spaced repetition for active recall #61 (flashcards/spaced repetition) or Replace meeting-shaped transcript extraction with concept-shaped extraction #63 (concept extraction) — this issue needs one of those to have something to track mastery of.