Add Streamlit demo: calculate pi from a geometric series

[telboth]

Summary

• Adds a standalone Streamlit demo under pi_calculator_demo/ that estimates π using the geometric series 1/(1+x²) = 1 - x² + x⁴ - x⁶ + ... (ratio -x²), integrated to give the Leibniz series π/4 = 1 - 1/3 + 1/5 - 1/7 + ...
• Sidebar slider controls the number of series terms N
• Live metrics show the current π estimate, the exact value, and the error
• Two Plotly charts visualize (1) convergence of the estimate toward π as N grows, and (2) the geometric series itself — the partial-sum curve vs. the exact 1/(1+x²) curve, where the area under each corresponds to π/4

This is a self-contained demo (own app.py, requirements.txt, README.md) and does not touch the existing bug-tracker app in this repo.

Test plan

• Verified the series math numerically (estimate converges to π with expected error order)
• Ran streamlit run app.py headlessly and confirmed it serves (HTTP 200) with no runtime errors
• Manually exercise the slider in a browser to confirm the charts update interactively

🤖 Generated with Claude Code

https://claude.ai/code/session_01Mf7j8zybAMpC7WPPuQ9DeU

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Generated by Claude Code