feat: refactor progress indicators to implement discount management (#379)

[frankrichard99]

Description

Refactored the Progress Indicators module to fully implement robust Discount Management. This changes the cart milestone tracker from a static layout to a fully reactive engine inside the EnrollmentCTA block, resolving suboptimal UX and satisfying production quality standards.

Related Issue

Closes #379

Type of Change

• Bug fix
• New feature
• Refactoring / Code quality improvement
• Breaking change
• Documentation update

Checklist

• Code follows project style guidelines
• Self-review completed
• No console errors
• Uses Lucide icons consistently
• Responsive design implemented
• Starknet best practices followed

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Refactor Summary & Implementation Details

Following the designated project implementation plan, the following structural changes were successfully executed:

1. Analysis & Core Functionality Implementation

• New Component (DiscountProgressBar.tsx): Designed a responsive, multi-tiered milestone indicator featuring dynamic state tracking (locked, live progress fill, and unlocked badge transitions). Fully supports dark mode styling using custom Tailwind tokens.
• Integrated Context Engine (EnrollmentCTA.tsx): Connected selected tier values directly to client-side state hooks to calculate global aggregate spend in real time on user interaction.

2. Comprehensive Quality Control & Testing

• Unit Testing (DiscountProgressBar.test.tsx): Validates initial empty states, precise floating-point rounding boundary conditions ($49.99 + $50.00$), aria attribute compliance, and full-unlock logic limits.
• Integration Testing (EnrollmentCTA.integration.test.tsx): Simulated complex user workflows across multiple card click variations to ensure zero regressions in layout or event bubble flows.

3. Standards & Compliance Performance

• Accessibility (a11y): Native accessibility compliance mapping via structural roles (role="progressbar", role="region") and deterministic aria-valuenow, aria-valuemin, and aria-valuemax boundaries.
• Performance Impact: Minimal resource overhead footprint. State mapping handles computation entirely on the client layout thread without triggering external REST or database API queries.

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Warning

⚠️ Infrastructure Status (Local Build Verification Pass)

During local verification execution, two pre-existing project baseline errors were flagged within unrelated domains:

1. Auth Route Mismatch (src/app/api/auth/login/route.ts): A type generic issue matching early exit handlers to response shapes.
2. Prerender Crash (/settings): Missing contextual tree structure (ThemeProvider) during static compilation loops.

These errors are entirely isolated from the course module scope. All isolated modules, tests, and standard assets introduced in this branch pass flawlessly.

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