Serve each article's Markdown at .md URLs (and via Accept: text/markdown)

/pages.md (front page /.md) serves the page's source Markdown — per-language
hybrid assembly, title injected as '# title' when the content has no h1 —
with the same ETag/Last-Modified/no-cache scheme as the HTML, which now
carries vary: accept. Pages advertise the counterpart via
<link rel=alternate type=text/markdown> and llms.txt links point at the
.md URLs.

docs/backend.md

@@ -10,8 +10,8 @@ Thin FastAPI assembly: lifespan (open the kanta database, load the file store, t
 - `files.py` — the `FileStore` and image derivative helpers, and the file routes: `/_api/files`, `/_f/`, `/_themes/`, `/_fonts/`, the favicon settings endpoints.
 - `api.py` — the editor REST API and WebSockets: `/_api/pages`, `/_api/structure`, `/_api/settings`, `/_api/toggle-task`, `/_api/translations`, `/_api/ws/editor`, and the translator channel `/_translate/{clientkey}`.
 - `tracking.py` — visit analytics: GeoIP, client enrichment, favicon fetching, debounced broadcasts, the `/_ws` activity socket, the admin stream `/_api/ws/analytics`, and the `/_a` viewer page.
-- `feeds.py` — machine-readable site exports: `/llms.txt` (Markdown site map for LLM agents), `/feed.json` (JSON Feed 1.1) and `/feed.xml` (RSS 2.0 + atom:link), all carrying every published article with full content (relative URLs absolutized), linked from every page's `<head>` and from the sitemap, and recorded in analytics like page GETs. Bodies are RAM-cached (keyed by base URL, cleared by `_invalidate_pages` like the page render cache) and served with a content-hash ETag (304 revalidation).
-- `pages.py` — the public content pages: `/`, `/sitemap.xml`, `/robots.txt` and the `/{path:path}` catch-all.
+- `feeds.py` — machine-readable site exports: `/llms.txt` (Markdown site map for LLM agents, linking each article's `.md` Markdown URL), `/feed.json` (JSON Feed 1.1) and `/feed.xml` (RSS 2.0 + atom:link), the feeds carrying every published article with full content (relative URLs absolutized), linked from every page's `<head>` and from the sitemap, and recorded in analytics like page GETs. Bodies are RAM-cached (keyed by base URL, cleared by `_invalidate_pages` like the page render cache) and served with a content-hash ETag (304 revalidation).
+- `pages.py` — the public content pages: `/`, `/sitemap.xml`, `/robots.txt` and the `/{path:path}` catch-all. Every article also has a Markdown counterpart: a `.md` suffix on the page URL (or an Accept header explicitly naming `text/markdown` on the plain URL — the HTML response carries `vary: accept`) serves the page's source Markdown (per-language hybrid assembly via `?lang=`/Accept-Language, page title injected as `# title` when the content has no h1, same ETag/Last-Modified scheme as the HTML). Pages advertise it with `<link rel="alternate" type="text/markdown">`.
 
 Route ordering is load-bearing and lives in `app.py`: the api/tracking/files routers are included BEFORE `frontend.route(app, "/")` is called — fastapi-vue inserts its file routes at the position where `route()` was called (during `load()` in the lifespan), so anything registered earlier wins. The content catch-all `/{path:path}` is included AFTER `frontend.route()` so that built frontend assets still take priority over content slugs. The `Frontend` is constructed with `spa=False` explicitly: it only serves the built files without a catch-all.