Add interactive GitHub Pages product interface

[simaba]

Summary

Adds a polished public product interface for Lean AI Ops while preserving the existing Python/Streamlit runtime.

Public interface

• responsive GitHub Pages UI with dark/light themes
• interactive DMAIC phase workspace
• evidence-health and phase deliverable views
• local-only deterministic starter brief (no API request or persistence)
• question-first analytics tool explorer
• interactive architecture inspector
• rendered links into deeper repository documentation

Architecture and reuse

• adds docs/project-manifest.json as a versioned, machine-readable product/interface contract
• adds docs/public-interface-contract.md to define truthfulness and runtime boundaries
• documents the dual Streamlit + GitHub Pages architecture
• extracts the existing Streamlit CSS unchanged into ui/theme.py, reducing responsibility in app.py

Deployment and quality

• adds a GitHub Pages workflow with immutable action SHAs
• PR validation runs with read-only permissions
• Pages/OIDC write permissions are scoped only to the deploy job
• adds static interface contract tests and JavaScript syntax validation
• adds sanitized sample data explicitly marked as demo-only

Important boundary

The GitHub Pages demo does not execute the Python assessment engine, call Anthropic, persist projects, run statistical calculations, or claim that hypotheses are validated findings. Full project generation and analytics remain in the Streamlit application.

Deployment note

After merge, the repository's Pages source must be set to GitHub Actions for the first deployment if it is not already configured.