docs: keep founder sales assets private

[abrichr]

What changed

• keeps buyer-facing offer, qualification, deployment, OEM, procurement, and security material on docs.openadapt.ai
• removes private founder-working assets from the public site: the editable SOW, competitive battlecards, internal ROI worksheet, and legal outlines
• removes unresolved founder placeholders and public promises about conversion credits or compliance dates
• repairs navigation and cross-links after the boundary change

The removed material is preserved in the private openadapt-internal repository by the companion PR.

Validation

• uv run mkdocs build --strict
• uv run python scripts/validate_docs.py
• uv run pytest -q (76 passed)