feat: Improve form accessibility (#38) and add CI coverage (#39)

[olatechy0]

Closes #38 - Form accessibility improvements:

• ContributorProfileCard: wrap in , add id/htmlFor/aria-* attributes, role=progressbar, aria-live region
• BountyFilters: wrap in , add aria-live filter count, aria-label on search and selects
• TaskFilter: wrap in , add aria-live filter count, inputMode hints, aria-label on selects
• Add accessibility test suites for all three components

Closes #39 - CI coverage integration:

• Add @vitest/coverage-v8 dependency
• Configure v8 coverage provider with lcov/text/html reporters
• Add test:coverage script to package.json
• Add coverage generation step to frontend-ci.yml workflow

What

Why

Closes #38

How

Testing

Breaking Changes

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Checklist

General

• Branch is up to date with main
• PR title follows Conventional Commits format (e.g. feat: add reputation system)
• PR description is complete with issue reference (Closes #<issue-number>)
• One logical change per PR (no unrelated changes bundled in)

Testing

• Tests added or updated to cover the changes
• All tests pass (cargo test for contracts, npm run build for frontend)
• No compiler warnings (cargo clippy -- -D warnings)

Documentation

• Public API changes are documented with /// doc comments (Rust) or JSDoc (TypeScript)
• CONTRIBUTING.md, README.md, or other docs updated if needed
• CONTRACT_API.md updated if contract interface changed

Code Quality

• Code follows the project style (cargo fmt / ESLint)
• No any types introduced in TypeScript
• No hardcoded secrets, keys, or environment-specific values

Smart Contract (if applicable)

• require_auth() called on all state-changing operations
• Events emitted for all state changes
• Storage keys don't collide with existing keys
• Deadline and input validation is complete
• No unintended token transfer paths introduced

Frontend (if applicable)

• Components are under 150 lines
• UI is responsive and accessible
• Screenshots or recordings included for visual changes