Documentation sweep: stale references and inconsistencies

[mmcky]

Stale references and inconsistencies across the docs. (PR #31 already fixed the @v1→@v0 versioning references; the items below remain.)

• D24 — containers/VALIDATION.md:9-13 references test-html-builder.yml, test-pdflatex-builder.yml, test-jupyter-builder.yml — none exist (unified into test-containers-lectures.yml).
• D25 — build-jupyter-cache/README.md:206 references templates/cache-standard.yml — doesn't exist.
• D26 — docs/ARCHITECTURE.md:283-285 lists Dockerfile.gpu / environment-gpu.yml — neither exists (GPU path is AMI-based, see docs/GPU-AMI-SETUP.md).
• D27 — Container size numbers inconsistent across README.md, docs/ARCHITECTURE.md, docs/CONTAINER-GUIDE.md. Pick one set.
• D28 — docs/MIGRATION-GUIDE.md "Quick Migration" shows a non-container example as recommended; align with the container-first templates.
• D29 — docs/QUICK-REFERENCE.md missing failure-artifact-name (build-lectures) and save-cache (restore-jupyter-cache) inputs.
• D30 — README.md:9 status line "Ready for testing with lecture repositories" is stale.
• D31 — README.md lecture-repo table inconsistent with PLAN.md (mentions lecture-python-programming.myst; missing lecture-dp).
• D32 — TESTING.md build-time table vs containers/VALIDATION.md — two sources of truth; pick one.
• D33 — TESTING.md mangled markdown / broken code fence (~L293).
• D34 — Full consistency sweep after the code fixes land.

Filed from the 2026-06-16 technical review.