Automatically version documentation assets to prevent stale caches

[csandanov]

Custom theme assets previously kept the same URLs after their contents changed, allowing caches to serve old CSS, JavaScript, logos, and favicons after a deployment. Both documentation versions now generate content-hashed filenames for these assets and reference them in rendered pages. Unchanged assets retain their URLs, while changed assets automatically receive new ones.

A shared MkDocs hook handles versioning, including repeated development builds. Logo styling supports the generated filenames, and CI runs asset-versioning tests. Existing source asset URLs remain available for compatibility. No cache-purge credentials or deployment purge step are required.

Validation:

• Both strict documentation builds and the 1.0 link check pass.
• Three asset-versioning tests, nine documentation export tests, and the documentation contract check pass.
• All 1,370 generated hashed asset references resolve to emitted files across both versions.
• Browser verification confirms the new stylesheet and logo URLs render correctly.
• git diff --check passes.