Run Etherpad by default: without it every topic page 500s

The legacy client requests an Etherpad session on every topic page whose
lesson has contents, without ever checking whether the lesson contains a
pad — controllers/topics.js collects `etherpadPads` and then ignores it.
With Etherpad unreachable the request fails, `validUntil` comes back
undefined, and `new Date(undefined * 1000)` makes Express reject the
session cookie: "option expires is invalid", rendered as a 500.

So Etherpad was only nominally optional. Moving it out of the `tools`
profile also matches the live deployment, which always runs it.

The topic pages that still 500 are courses the signed-in user is not a
member of; the same page returns 200 for its own teacher. That is the
legacy client rendering a 403 as a 500, upstream behaviour we don't own.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

local-instance/docker-compose.yml

@@ -6,7 +6,7 @@
 # behaviour under test is the deployed behaviour, not a rebuild of main.
 #
 #   docker compose up -d                      core: login, courses, boards, files
-#   docker compose --profile tools up -d      + etherpad, h5p, tldraw, collabora
+#   docker compose --profile tools up -d      + h5p, tldraw, collabora
 #   docker compose --profile av up -d         + virus scanning of uploads
 #
 # Everything here is a throwaway dev instance: the credentials are the upstream
@@ -162,6 +162,26 @@ services:
     ports: ["127.0.0.1:4000:4000"]
     restart: unless-stopped
 
+  etherpad:
+    # The collaborative text editor element.
+    #
+    # Core, not a "tool", however much it looks like one: the legacy client asks
+    # the server for an Etherpad session on *every* topic page whose lesson has
+    # contents, without checking whether the lesson contains a pad at all
+    # (controllers/topics.js builds `etherpadPads` and then never reads it).
+    # Unreachable, that call fails, `validUntil` arrives undefined, and
+    # `new Date(undefined * 1000)` makes Express reject the session cookie —
+    # "option expires is invalid", a 500 on every topic page. The live
+    # deployment always runs Etherpad (ETHERPAD_REPLICAS: 1), so keeping it in
+    # the default profile is both the working and the faithful choice.
+    image: docker.io/etherpad/etherpad:3.3.3
+    env_file: [env/etherpad.env]
+    volumes:
+      - ./etherpad/APIKEY.txt:/opt/etherpad-lite/APIKEY.txt:ro
+    depends_on:
+      mongo: {condition: service_healthy}
+    restart: unless-stopped
+
   proxy:
     # The single origin. Everything a browser touches goes through here, so the
     # app sees one host the way it does in production.
@@ -173,17 +193,6 @@ services:
     restart: unless-stopped
 
   # -------------------------------------------------- external tools ------- 
-  etherpad:
-    # The collaborative text editor element on column boards.
-    image: docker.io/etherpad/etherpad:3.3.3
-    profiles: ["tools"]
-    env_file: [env/etherpad.env]
-    volumes:
-      - ./etherpad/APIKEY.txt:/opt/etherpad-lite/APIKEY.txt:ro
-    depends_on:
-      mongo: {condition: service_healthy}
-    restart: unless-stopped
-
   h5p-editor:
     image: quay.io/schulcloudverbund/h5p-server:${SC_VERSION:-33.40}
     profiles: ["tools"]