Assess optional Markdown output strategy for Sphinx/ReadTheDocs docs build

[Copilot]

This issue asked whether the docs build can optionally emit Markdown instead of the current HTML output, and how difficult that would be. This PR captures a feasibility assessment and implementation plan without introducing behavior changes yet.

• Current state analysis

  • Confirmed the docs pipeline is Sphinx-based and pinned to sphinx==3.0.0.
  • Confirmed current RTD/local flow is HTML-first (make html / Sphinx HTML builders), with RTD also configured for PDF.

• Markdown feasibility findings

  • Identified that the current pinned Sphinx version does not provide a native Markdown builder path suitable for immediate use.
  • Documented practical constraints from current extensions/theme/version pins that affect Markdown output strategy.

• Implementation options proposed

  • Option A (low disruption): keep current HTML build and add optional HTML→Markdown conversion (e.g., Pandoc post-processing).
  • Option B (higher fidelity, higher risk): upgrade Sphinx and adopt a Markdown-capable builder extension.
  • Option C (not recommended): custom builder/plugin due to maintenance cost.

• Recommended execution plan

  • Phase 1 spike on Option A to produce sample Markdown output and validate link/image fidelity.
  • Promote to optional build target (make markdown) only if output quality is acceptable; otherwise proceed to Option B.

# current baseline build
cd docs
make html

# proposed optional path (conceptual)
make markdown