docs/template_context.rst is generated by cog from the manifest in
datasette/template_contexts.py, following the json_api_doc.py pattern.
It documents the base context available on every page plus the
database, query, table and row pages, including the stability policy
for custom template authors.
Refs #2127
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
