Improve researcher documentation entrypoint

[joanjcaceres]

Summary

• Refactor the internal BBQ linear solve into readable stages that mirror the matrix quantization derivation: frozen-variable Schur reduction, positive-capacitance projection, free-coordinate charge-sector reduction, final frequency eigenproblem, and branch ZPF calculation.
• Add BBQ Implementation Notes mapping the derivation and notation directly to the current helper stages in sccircuits/bbq.py.
• Add BBQ Validation documenting code-backed trust checks from tests/test_bbq.py: LC units/ZPF, generalized eigenproblem normalization, frozen-coordinate reconstruction, free/zero-potential reduction, null capacitance, branch sign, and cQEDraw row order.
• Expose the trust pages through MkDocs navigation, the BBQ overview, examples page, and README starting points.
• Clarify that the configured GitHub Pages URL is not considered launched until it returns 200 OK after the Pages deployment is merged/enabled.

Closes #70

Launch / discoverability checklist

• Merge the documentation deployment workflow to main.
• Ensure GitHub Pages is enabled for the repository.
• Verify https://joanjcaceres.github.io/sccircuits/ returns 200 OK after deployment.
• Add the same URL to the GitHub repository sidebar website field.
• Confirm README and pyproject.toml point to the live documentation URL.

Verification

• pixi run -e sccircuits docs-build
• pixi run -e sccircuits test
• pixi run -e sccircuits typecheck
• pixi run -e sccircuits lint
• git diff --check

Notes

• The current public docs URL returned 404 before this PR was merged/deployed, so the final URL check remains a post-merge deployment step.
• The untracked top-level test_bbq.py in the local worktree was not included.

[joanjcaceres]

Process note: attempted to request GitHub Copilot review with gh pr edit 71 --add-reviewer "@copilot" using /opt/homebrew/bin/gh version 2.79.0, but GitHub returned @copilot not found; retrying as copilot also returned copilot not found. Review request is therefore not attached.