Restore the original Overview rendering contract: the
`instance.overview` (`AGNES_INSTANCE_OVERVIEW`) HTML body renders
verbatim via `| safe` filter, just inside the welcome hero's
`.home-hero-footnotes` styled block instead of as a standalone
`<section class="home-overview">` between the walkthrough and
surfaces grid. Only the location and styling moved — existing
instances that set the yaml field get the same content in the
new home.
Tests updated accordingly: footnotes render the operator's HTML
marker when the flag is set (mirrors the previous
`test_overview_section_renders_when_yaml_set`), and are absent
when the flag is empty (mirrors `test_overview_section_hidden_when_yaml_empty`).
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