chore: upgrade backend and frontend dependencies

[0x2E]

Summary

• Upgrade feedfinder to v0.1.2 and align gofeed to v1.4.0 (better malformed-feed parsing, data-race fix).
• Bump other direct backend modules: gin, go-oidc, modernc.org/sqlite, x/crypto, x/oauth2, x/sync, go-isatty.
• Upgrade frontend patch/minor deps (React, Vite, Tailwind, TanStack, ESLint stack, lucide-react, fonts, shadcn CLI).

Test plan

• go build ./... and go test ./... in backend/
• npx tsc -b --noEmit and pnpm build in frontend/
• Smoke-test feed discovery / add-feed flow (feedfinder path)
• Smoke-test login and article list in the UI