No support for Authors and Translator attribution per lecture

[mmcky]

The theme has no equivalent of quantecon-book-theme's authors option, and no notion of translators at all. Raised during the theme evaluation in QuantEcon/lecture-python-programming#475 (closed, never merged).

How this surfaced. Porting the QuantEcon Python Programming lecture config to this theme meant deleting the authors block outright, because there was nothing to map it onto:

quantecon-book-theme	quantecon-sphinx-theme
authors: — list of {name, url} pairs, rendered per lecture	no equivalent; dropped in the port
—	no translator concept exists in either theme

What's wanted. Author and translator attribution rendered per lecture page. Translators matter specifically because the QuantEcon lecture series are translated into several languages (zh-cn, fa, fr), and translator credit currently has nowhere to live in either theme.

Design questions worth settling first

• Is attribution per-page (front-matter driven) or per-project (html_theme_options driven), or both, with page-level overriding project-level?
• Where does it render — under the page title, in the footer, or both?
• Does this belong in a brand-neutral theme at all, or is it QuantEcon-specific? PLAN.md positions this theme as deliberately brand-neutral with "minimal opinion", but per-page authorship is a general scholarly-documentation need, not a QuantEcon one. Worth deciding explicitly rather than by default.
• If it lands here, does quantecon-book-theme eventually inherit it, per the PLAN.md goal of this theme becoming the upstream base?

[mmcky]

Now tracked as part of the cross-theme effort in QuantEcon/project-themes#3, alongside QuantEcon/quantecon-book-theme#426 and QuantEcon/quantecon-theme.mystmd#143. The shared design questions raised here (page- vs project-level, placement, brand neutrality) are being settled in the tracking issue so the three themes stay consistent.