feat(jellyfin): big-screen theme for the TV, mounted into the wmc slot

serverAppConfigs-docs/Dankserver/Jellyfin.md

@@ -407,6 +407,41 @@ removed. Discover a route's verb from the `Allow` header of an `OPTIONS` (or
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   never confirmed), so revoke by token and never by app name.
 
+## Big-screen theme (the TV)
+
+`dankserver/jellyfin/theme/wmc/theme.css` is repo-owned and bind-mounted over the
+image's **Media Center** theme slot (the `Volume=` line in
+`dankserver/jellyfin/quadlet/jellyfin.container`). It exists for
+`danklivingroom`, which renders this server-served web app at 3840×2160 with no
+client-side scaling, so 14 px text arrives on a panel read from three metres.
+
+The file is four rules, and its first line is the design:
+`@import url("../dark/theme.css")` pulls in the **live upstream** dark palette, so
+the repo never vendors a CSS snapshot and a Jellyfin image bump cannot strand one.
+That works because jellyfin-web applies a theme as
+`<link rel="stylesheet" href="themes/<id>/theme.css">` — a relative URL resolved
+against the CSS file, not the document. The size lives in one number:
+`--dank-big-screen-zoom` (1.75 ≈ three metres; 1.5 mild, 2.0 projector). `zoom` on
+the root element is the right lever: the card-grid code measures layout pixels, so
+fewer, larger columns are computed rather than overflow produced.
+
+- **Adoption is per device, and it stays that way.** The theme a client renders
+  comes from its own settings (localStorage first), so there is no server-side
+  "everyone gets the big UI" knob. On the screen that wants it:
+  **Display Settings → Theme → Media Center.** That is also the honest label —
+  the dropdown names are compiled into the bundle, so a "Big Screen" entry will
+  never appear; do not go looking for one.
+- The mount is `:ro` and the app only fetches the file, so the failure mode of a
+  stale `@import` target is slightly wrong colors, never a dead web app.
+- **Editing the CSS needs no restart.** The bind hands out the host file's live
+  bytes, so a changed zoom number is on screen at the next page load. The planner
+  agrees by construction: only `dankserver/<svc>/quadlet/**` maps to a service, so
+  a `theme/**`-only commit plans nothing — that is correct, not a gap to "fix",
+  because restarting a media server for a font size is the wrong trade. Only the
+  first deploy of the `Volume=` line restarts anything.
+- **Rollback is one line:** drop the `Volume=` and redeploy; nothing in the
+  database records the theme, so no cleanup follows.
+
 ## See Also
 
 - [[Plex]] — co-resident media server on the same volume