publishing: deploy the docs to their own Surfer app at docs.inference.coop

The docs now have a dedicated Cloudron app (io.cloudron.surfer,
location docs.inference.coop, id 85b7ce06-e2af-49a4-bd4f-a9c2e692e3ab)
serving /app/data/public. deploy.sh writes there and nowhere else; the
two copies inside the marketing Surfer app (public-docs and
public/docs) have been deleted, so there is one canonical location.

SURFER_APP now defaults to docs.inference.coop and DOCS_DEST to
/app/data/public.

publishing/README.md

@@ -2,7 +2,8 @@
 
 The Markdown in this repository is the single source of truth. This directory
 is the publishing layer that turns it into a member-readable static site and
-puts it on the co-op's Surfer app. Documents are never edited here — a change
+puts it on the co-op's docs Surfer app at https://docs.inference.coop/.
+Documents are never edited here — a change
 to a document is a normal commit or pull request against the Markdown at the
 repository root.
 
@@ -40,18 +41,24 @@ CI-style runs should use, so broken links fail the build.
 CLOUDRON_TOKEN=... publishing/deploy.sh
 ```
 
-Writes the build into the Surfer app (Cloudron app `inference.coop`) at:
+Writes the build into the **docs Surfer app** (Cloudron app `docs.inference.coop`,
+`io.cloudron.surfer`) at:
 
-- `/app/data/public-docs/` — served at **https://docs.inference.coop/**
-- `/app/data/public/docs/` — served at **https://inference.coop/docs/**
+- `/app/data/public/` — served at **https://docs.inference.coop/**
 
-Both are written so the site stays reachable either way; the hostname is the
-canonical one.
+That is now the one canonical location. The docs used to be a pair of
+directories inside the *marketing* Surfer app (`inference.coop`) as well, at
+`/app/data/public-docs/` and `/app/data/public/docs/`; both were deleted when
+this app took over, so `https://inference.coop/docs/` no longer serves the docs
+(nothing on the marketing site linked to it).
+
+Override the destination with `SURFER_APP` (the app's Cloudron location) and
+`DOCS_DEST` (path inside the container) if you ever need to.
 
 ## Automatic rebuilds (push to main)
 
 Two mechanisms keep the site in step with `main`; both run on the agent host
-and neither adds a Cloudron app.
+and deploy into the docs Cloudron app above.
 
 **Polling (running now).** `docs-deploy-poll.service` polls Gitea every 60
 seconds and deploys whenever `main` moves. A push appears on the site within