Mark closed upstream GitHub issues in rewards feed

[Utkarsh2726]

Closes #55

Summary

• Adds a small GitHub issue-state reconciler for rewards loaded into the home feed.
• Marks upstream GitHub issues as closed when the public GitHub API reports state: "closed".
• Shows a Closed upstream badge on affected reward cards and disables the claim action in the reward detail panel.
• Keeps pagination based on the raw backend response length so marking closed items does not prematurely stop infinite scroll.
• Tolerates GitHub API failures by leaving the existing reward unchanged instead of breaking the feed.

Validation

• node_modules\.bin\vitest.cmd run app\_utils\reconcileGithubIssueState.test.ts app\home\_components\ClaimRewardModal.test.tsx
• node_modules\.bin\tsc.cmd --noEmit
• node_modules\.bin\eslint.cmd app\_utils\reconcileGithubIssueState.ts app\_utils\reconcileGithubIssueState.test.ts app\_utils\getRewards.ts app\_core\_dtos\IssueListDTO.ts app\home\view.tsx app\home\_components\HomeRewardCard.tsx

Lint note: targeted lint has 0 errors and 2 pre-existing image warnings in HomeRewardCard.tsx. Whole-project lint is blocked by existing CRLF line-ending errors across many untouched files.