chore: upgrade to 7.3.0+v1.154.0

- matrixdotorg/synapse: v1.149.1 -> v1.154.0
- pgautoupgrade/pgautoupgrade: 17-alpine -> 18-alpine (+ PGDATA pin for in-place upgrade)
- ghcr.io/element-hq/matrix-authentication-service: 1.14.0 -> 1.18.0
- nginx: 1.29.6 -> 1.31.1
- discorddb postgres: 13-alpine -> 16-alpine (conservative bump; manual dump/restore required)

Deferred to separate PR:
- mautrix/signal v0.8.7 -> v26.02.2 (CalVer; requires signaldb dump/restore)
- mautrix/telegram v0.15.3 -> v0.2605.0 (CalVer; requires telegramdb dump/restore)
- signaldb/telegramdb postgres: 13-alpine (deferred with bridges)

compose.discord.yml

@@ -30,7 +30,7 @@ services:
       - internal
 
   discorddb:
-    image: postgres:13-alpine
+    image: postgres:16-alpine
     secrets:
       - discord_db_password
     environment:

compose.mas.yml

@@ -5,7 +5,7 @@ version: "3.8"
 
 services:
   mas:
-    image: ghcr.io/element-hq/matrix-authentication-service:1.14.0
+    image: ghcr.io/element-hq/matrix-authentication-service:1.18.0
     command: ["server", "--config=/etc/mas/config.yaml"]
     environment:
       - DOMAIN

compose.yml

@@ -3,7 +3,7 @@ version: "3.8"
 
 services:
   web:
-    image: nginx:1.29.6
+    image: nginx:1.31.1
     networks:
       - proxy
       - internal
@@ -43,7 +43,7 @@ services:
       start_period: 2m
 
   app:
-    image: "matrixdotorg/synapse:v1.149.1"
+    image: "matrixdotorg/synapse:v1.154.0"
     volumes:
       - "data:/data"
     secrets:
@@ -114,7 +114,7 @@ services:
       restart_policy:
         condition: on-failure
       labels:
-        - "coop-cloud.${STACK_NAME}.version=7.1.1+v1.149.1"
+        - "coop-cloud.${STACK_NAME}.version=7.3.0+v1.154.0"
         - "coop-cloud.${STACK_NAME}.timeout=${TIMEOUT}"
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:8008/health"]
@@ -124,10 +124,14 @@ services:
       start_period: 1m
 
   db:
-    image: pgautoupgrade/pgautoupgrade:17-alpine
+    image: pgautoupgrade/pgautoupgrade:18-alpine
     secrets:
       - db_password
     environment:
+      # postgres:18 relocated default PGDATA to /var/lib/postgresql/18/docker.
+      # Pin to legacy path so pgautoupgrade finds the existing cluster and
+      # upgrades in place instead of init-ing an empty one.
+      - PGDATA=/var/lib/postgresql/data
       - LC_COLLATE=C
       - LC_CTYPE=C
       - POSTGRES_DB=synapse