feat: add bounty loading states

[tolga-tom-nook]

Summary

• Adds src/bounty-loading.js for bounty list loading, loaded, empty, and error states.
• Shows an accessible spinner (role="status", aria-live="polite") while the API call is pending.
• Removes the spinner once data loads and renders bounty results.
• Handles empty and failed API responses gracefully with explicit states and safe escaped error markup.
• Adds tests covering spinner rendering, successful load cleanup, empty state, error state, and HTML escaping.

Validation

• npm test
• Result: 20 passed, 0 failed

Fixes #18

BountyPay payout setup

Bounty: $50 USD1
Wallet: 0x4a76c7E64C08cF29B59eFC640b4ada97A270d428
Chain: BSC / BNB Smart Chain
Issues: #18

[tolga-tom-nook]

BountyPay payout setup for PR #77

BountyPay payout setup for issue #18.

Bounty: $50 USD1
Wallet: 0x4a76c7E64C08cF29B59eFC640b4ada97A270d428
Chain: BSC / BNB Smart Chain
Issues: #18