feat: robust GitHub issue tracking + user feedback UI

[VibhavSetlur]

Summary

This PR adds two complementary features:

1. GitHub Issue Tracking System (.github/)

• 5 GitHub Issue Forms YAML templates: bug report, feature request, documentation, question, and template chooser config
• Templates include ModelSEED-specific dropdowns (environment: staging/prod/localhost; area: FBA/Gapfill/Model viewer/Biochem/Media/Genomes/Auth/Other; auth status)
• PULL_REQUEST_TEMPLATE.md with staging-aware CI checklist
• CODEOWNERS assigning @VibhavSetlur as default reviewer

2. Website Feedback UI

• FeedbackFAB: auth-gated floating action button mounted in root layout
• FeedbackDialog: MUI Dialog with bug/feature/question form; two CTAs — "Open GitHub Issue" (prefills the new issue form via URL params) and "Submit Feedback" (POSTs to backend via proxy)
• app/api/feedback/route.ts: Next.js proxy to ${MODELSEED_REST_URL}/feedback, mirroring the /comments pattern
• FooterFeedbackButton: client wrapper added to Footer.tsx for future use
• Vitest unit tests for buildGitHubIssueUrl()

Verification

• npm run lint ✅
• npx tsc --noEmit ✅
• npm run test:run ✅ 125 tests (3 new)
• npm run build ✅

Notes

• Footer.tsx edit is spec-correct but the component is currently orphaned (not rendered anywhere); the FAB is the live entry point
• Backend /feedback/ payload is undocumented — proxy mirrors /comments convention defensively