Improve static site generator settings

[MicrowaveDev]

Source of truth

Improve static site generator settings without redesigning the static-site protocol. The current first slice is backend validation and persistence: generated sites should use normalized settings, reject invalid static-site names, keep custom CSS bounded, and store the exact normalized options used for rendering.

Scope

• Normalize numeric render settings before generation: post title length, post description length, and posts per page.
• Validate nested site.name, not only legacy top-level name.
• Bound stylesCss to a string payload with a size limit before appending it to generated CSS.
• Create group static-site records after group defaults are merged, so generated pages and stored options use the same settings object.
• Preserve custom CSS support and persist normalized render options in StaticSite.options.
• Return static_site_not_found for missing static-site updates instead of dereferencing a missing record.
• Update docs/todo.md with the active settings slice.

Verification

• Static-site generator tests for normalized settings, custom CSS persistence, invalid names, and missing update targets.
• npm run test:docker