chore(images): pin service image updates

Replace floating service images with reviewable tags or digests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

gitea/compose.yaml

@@ -1,6 +1,6 @@
 services:
   server:
-    image: docker.gitea.com/gitea:1.26
+    image: docker.gitea.com/gitea:1.27.3
     container_name: gitea
     restart: always
     environment:
@@ -61,7 +61,7 @@ services:
     depends_on:
       - db
   db:
-    image: docker.io/library/postgres:14
+    image: docker.io/library/postgres:14.24-alpine
     restart: always
     environment:
       - POSTGRES_USER=gitea