Per-page announcements (additive follow-up to the site-wide banner)

Background

The dismissible announcement banner shipped as site-wide only — a single announcement (plus optional announcement_expires) theme option rendered at the top of every page. See the Announcement Banner docs.

The renderer was deliberately built to be additive: the template loops over a list of notices, announcement.js evaluates each .qe-announcement row independently (its own content-hash dismissal + its own expiry), and the dismissed-set in localStorage already tracks multiple IDs. So the JS, persistence, and most of the CSS already support N rows. What's left for per-page is the config plumbing, a little stacking polish, and one design decision.

Goal

Let an individual page carry its own announcement that stacks additively with the global one: global on top, page-specific below. Example use case — flagging that a single lecture now uses a newer library version (pandas==3.0) while a site-wide notice (an Anaconda upgrade) stays visible.

Open decision: how should a per-page notice be authored?

My current lean is to re-evaluate frontmatter for per-page, since page-specific content arguably belongs with the page — but this is the thing to settle before building.

Settled design (for whichever mechanism wins)

• Additive: when both global and per-page are present, render two stacked rows (global first).
• Each row independent: its own expiry, its own × dismiss, its own content-hash so editing one re-shows only that one.
• When a page has only one of the two, show just that one; when all rows are dismissed/expired, the bar collapses.

Scope / priority

Demand-driven — open this when there's a concrete need. The site-wide banner already covers the primary case.

Start with docs/user/announcements.md and the existing announcement.js behavior described in the issue, then inspect the template and theme-option plumbing. Resolve whether per-page notices use an announcements map or MyST frontmatter before implementation. Done means global and page notices stack in order, dismiss and expire independently, and the bar collapses when no rows remain.