feat: add ui for assets page

[Jetshree]

What does this PR change?

This PR implements a complete Assets page for the OpenCost UI with comprehensive cost visualization and analysis capabilities.

TypeScript-Driven Architecture

• TypeScript setup: Enabled tsconfig.json with strict mode scoped to new .ts/.tsx files for safe incremental migration.
• Centralized type contracts: Defined shared interfaces for assets APIs, charts, KPIs and component props.
• Safer development workflow: Improved type safety early error detection refactoring confidence and IDE intelligence.
• Stable UI state model: Implemented persistent filters and unified Loading Empty and Error primitives.
• Layered SCSS architecture: Used global.scss with variables mixins and nested structures to integrate cleanly with Carbon while avoiding hard overrides.

Design System & UI Alignment

• Carbon adoption: Built the entire Assets page using @carbon/react components.
• Chart integration: Implemented five analytics charts using Carbon.
• Icon standardization: Used Carbon icons for asset types and actions.
• Consistent UI states: Applied Carbon-native skeleton, empty, and error patterns across all views.

Dashboard Capabilities

• KPI insights: Delivered four computed tiles highlighting cost and carbon signals.
• Analytics layer: Added five charts covering trends, breakdowns, distribution, and emissions.
• Advanced table: Built searchable, sortable, paginated DataTable with CSV export.
• Drill-down analysis: Enabled inline asset detail view with trend and efficiency metrics.

Data & Tooling Enhancements

• Typed service layer: Implemented a robust TypeScript service in src/services/assets.ts that wraps four backend endpoints with integrated mock data fallback.
• Performance optimization: Optimized data fetching in src/pages/Assets.tsx using parallel Promise.all calls with isolated refetch logic for granular chart updates.
• Development support: Added mock dataset covering major asset types and providers.
• Strict compilation: Ensured tsc --noEmit passes with zero errors.

How will this PR impact users?

Users will get a clean and simple interface that shows them the main analysis at a glance. They won't get overwhelmed by a complex UI, but they can still use filters to find the specific data they need. I designed the interface to follow a simple Detect → Analyze → Act workflow:

• Detect: KPIs at the top let users spot problems immediately.
• Analyze: Charts in the middle help users investigate trends.
• Act: Detailed tables at the bottom provide the specific data needed to take
  action.

Does this PR address any GitHub or Zendesk issues?

• Closes ... [LFX Mentorship Term 1 2026] OpenCost UI Revamp #155 Support Assets in the UI #28

How was this PR tested?

• Verified all charts render correctly with mock data
• All files compile without errors
• Tested filters, table search, pagination, drill-down view, and CSV export.
• Validated mock fallback and loading empty and error states across the page.
• tsc --noEmit passes with strict: True
• All new components and API contracts fully typed

Does this PR require changes to documentation?

• Yes

Have you labeled this PR and its corresponding Issue as "next release" if it should be part of the next OpenCost release? If not, why not?

• No. While this PR addresses the requirements of the coding challenge, it is currently intended for evaluation purposes. If accepted, I plan to refine this code further and a final architectural discussion with mentors to ensure it meets all production standards before being slated for an official release.

Demo video

ui_demo.mp4

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[ameijer]

Thank you for your application to our Term 1 Mentorship! We had so many amazing submissions that met and exceeded all our application criteria; this was the hardest mentee selection process we have had to go through. This means that there were many excellent applicants who did great work and correctly implemented the programming challenge, but we could only ultimately select one applicant. Unfortunately, were were unable to move forward with your application.

We hope you will consider applying to one of our future mentorship terms! in the meantime, we are always grateful for any contributions you want to make to OpenCost!.

Thanks again,
Alex, on behalf of the OpenCost Mentors