fix: add frontend agent request timeouts

[saurabhhhcodes]

Summary

• add a shared 5-second frontend agent request timeout
• apply the timeout to search and product info POST calls
• document the timeout behavior in the frontend integration README

Fixes #148

Verification

• git diff --check
• python3 -c "from pathlib import Path; compile(Path('frontend-integration/frontend_app.py').read_text(), 'frontend-integration/frontend_app.py', 'exec'); print('syntax ok')"
• mocked Flask test-client check that both POST routes pass timeout=5 and timeout failures return JSON errors

[gautammanak1]

Thanks for the contribution 🚀

The CI for this PR is currently failing. Please fix the following so we can move forward:

• changelog-check — add an entry to contributors/CHANGELOG.md (community agents) or root CHANGELOG.md
• format — run ruff format . and commit the result
• lint — run ruff check . --fix and resolve remaining warnings
• stargazer-gate — please ⭐ star this repository (the gate passes once you've starred)

Once the checks are green it'll be ready for maintainer review. Let me know if you need any help! 🙌