Build Unraid image directly from the Gitea repo

docker-compose.unraid.yml now uses a Git URL as the build context
(https://git.oservr.com/ort/KCal.git#main) instead of requiring a manual
clone onto the array — Docker/BuildKit fetches the source itself at build
time. Requires the repo to allow anonymous HTTP read access in Gitea
(Settings -> Visibility -> Public); this is a read-only clone, nothing
more. Verified with a real docker build/compose run against the public
repo, not just syntax-checked.

UNRAID.md rewritten to match: no deploy key, no NerdTools/git, no source
checkout needed. Kept a token-auth alternative documented for anyone who'd
rather keep the repo private.

docker-compose.unraid.yml

@@ -1,6 +1,13 @@
 services:
   kids-calendar:
-    build: .
+    build:
+      # Docker/BuildKit clones the repo itself at build time — no manual
+      # git clone onto the array needed. Requires the repo to allow
+      # anonymous HTTP read access in Gitea (Settings → Visibility →
+      # Public); this is a read-only clone, so nothing beyond that is
+      # needed. #main is the branch to build from.
+      context: https://git.oservr.com/ort/KCal.git#main
+      dockerfile: Dockerfile
     container_name: kids-calendar
     ports:
       - "3007:3007"