Enhance README with architecture and logic flow diagrams

[Nitya-003]

Summary of Changes

This PR introduces a dedicated Architecture & Logic Flow section to the README.md. As Proofolio processes complex data streams from GitHub, LinkedIn, and Blogs, these diagrams provide a "birds-eye view" for SWOC '26 contributors to better understand the system's integration points.

Key Visualizations Added:

1. System Data Flow: Highlighting the relationship between External APIs, the React Frontend, and the Supabase Backend/AI Engine.
2. Authentication Lifecycle: Detailng the Supabase Auth flow and JWT session persistence within the React Context API.
3. Report Generation Pipeline: Visualizing the data transformation from raw stats to Recharts and finally to PDF via jsPDF.

Type of Change

• chore (Documentation enhancement for SWOC '26)

Proof of Work

I have verified that the Mermaid.js blocks render correctly in both GitHub Dark and Light modes.

Checklist

• My PR contains exactly one commit (squashed).
• I have followed the SWOC Project Admin (PA) Playbook for documentation standards.
• I have verified the diagrams accurately reflect the current project structure.

Related Issue

Closes #68

[vercel]

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