Read a report with its sections and widgets

Returns the header of the report and, section by section, its widgets: what each one is, where it reads from, and either its definition in the widget DSL or the named reason it has none. A widget that carries no data -- a text block, an image, a page break -- is never editable, and neither is one whose definition uses something the DSL cannot say. The answer is bounded at 500 widgets and is cut on a section boundary when the report has more, with truncated: true. The sections of a template_based report are its template's. It also carries settings, the settings window of the report -- brand template, front cover, PDF options, localization, language file, substitution variables, what the widgets show, the snapshot switch and the AI brief -- in the same shape /v1/reports/update takes it, with the names of the brand template and of the language file resolved. The uploaded file of the cover is published by name only: its content never travels here. The listings do not carry the block.