Fix immich v3 storage dirs, revert discourse and zulip to previous slots

- immich: add init container to create required upload subdirectories
  (thumbs, upload, backups, library, profile, encoded-video) for v3
- discourse: revert to slot 3 (v3.5.3) — 2026.x image changed internal
  build system, needs full template rewrite to work as plain container
- zulip: revert to slot 9 (v9.4) — 12.x renamed all env vars
  (DB_HOST -> SETTING_REMOTE_POSTGRES_HOST, etc.), needs template rewrite

immich/versions/3/deployment-microservices.yaml

@@ -21,6 +21,18 @@ spec:
         runAsUser: 1000
         seccompProfile:
           type: RuntimeDefault
+      initContainers:
+        - name: init-dirs
+          image: "ghcr.io/immich-app/immich-server:v3.3.5"
+          command: ["sh", "-c", "mkdir -p /usr/src/app/upload/thumbs /usr/src/app/upload/upload /usr/src/app/upload/backups /usr/src/app/upload/library /usr/src/app/upload/profile /usr/src/app/upload/encoded-video"]
+          securityContext:
+            allowPrivilegeEscalation: false
+            capabilities:
+              drop: [ALL]
+            readOnlyRootFilesystem: false
+          volumeMounts:
+            - mountPath: /usr/src/app/upload
+              name: immich-storage
       containers:
         - image: "ghcr.io/immich-app/immich-server:v3.3.5"
           name: immich-microservices