exercise architecture, migrate interval classifier

Created by: jedmund

Summary

Lays down a shared architecture for scored exercises and migrates the first two off the old ad-hoc pattern (Interval Classifier, Interval Trainer). Adds a new app icon along the way.

Shared exercise architecture

• ExerciseState tracks progress and results; ScoringOverlay wraps content with progress dots and a completion screen; PickerWidget handles multiple-choice answers with adaptive grid columns (2 / 3 / 4 based on choice count).
• ExerciseLayoutContext environment switches exercises between standalone (centered glass card) and lesson-page (context text above card) presentations without duplicating views.
• ExerciseHost, InteractionWidget, and ToolBridge are scaffolding for future exercises that drive a tool. Not yet wired — we intentionally deferred ToolBridge until a keyboard-driven exercise forces its design.
• ProgressDotsView reworked: filled circles with design tokens (.accentColor / .incorrectWarm), visible on glass.
• ActivityStateRegistry.scoredExerciseState(for:) + progressStore integration so progress survives navigation and gets persisted across sessions.

Interval Classifier

• Rebuilt on the shared stack. Static-prompt JSON, categorical answers.
• New design baseline: glass card, .thinMaterial picker buttons, centered feedback with inline bold answer, filled-circle feedback icon matching progress dots, small capsule Next button, progress dots hidden during feedback state.
• Old IntervalClassifierView and its ToolViewFactory case removed.

Interval Trainer

• Same visual baseline as Interval Classifier.
• First exercise with procedural prompt generation (random root in range + random interval from active pool). ExerciseState handled it without changes, confirming the model is generation-agnostic.
• Streak-based interval unlocks preserved (silent, no toast). Streak/unlock bookkeeping stays local to the exercise view — it's domain-specific, not universal.
• IntervalTrainerConfig gained a context field (the lesson JSON already had one that was being silently dropped).
• Old IntervalTrainerView and its ToolViewFactory case removed.

App icon

• New waveform glyph on cream. Dark/tinted slots registered but unfilled for now (fall back to default). Build number bumped to 3.

Test plan

• Standalone Interval Classifier: Exercises grid → tap → listen, pick, advance, complete. Retry from completion resets dots.
• Standalone Interval Trainer: Exercises grid → tap → same loop. After 3 correct, new intervals silently appear in the picker; grid stays readable.
• Lesson with each exercise: context text renders above card, progress persists across navigation away and back.
• Exercise completion records an attempt via progressStore and allows scrolling past the gate.
• App icon renders in Springboard and reflects correctly on TestFlight / App Store Connect upload.