Handle proxy restrictions for live data

[bowenzhengzbw]

Summary

• add an HTTP helper that retries Yahoo Finance requests without proxies before falling back to environment proxy settings
• wire the suggestion endpoint and analysis fetches through the new helper so autocomplete and data retrieval work in restricted networks
• document the proxy failover behaviour and troubleshooting guidance in the README

Testing

• python -m compileall app.py

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https://chatgpt.com/codex/tasks/task_b_68e6229c78b08323906ce091c0483290