Fix CI port collision — remap throwaway Postgres to host port 15432

The runner host typically has another Postgres listening on 5432
(local dev stack, stage instance, etc.), which made the services:
postgres container fail at start with "port already allocated."

Remap the host-side port from 5432:5432 to 15432:5432. The service
container still listens on 5432 internally; only the runner host
binding changes. Dry-run's DB_PORT updated to 15432 to match.

--network host semantics preserved: DB_HOST=localhost reaches the
service on the runner's loopback at the new port.

Why we still need a Postgres container at all: the dry-run gate
applies db-init/*.sql migrations and the directus schema snapshot
against a real DB to catch breakage before pushing the image. No
Postgres = no validation = the gate is bypassed.

Inline comment in the workflow now explains the choice; task spec's
Done section captures the correction so future readers don't
re-discover this.

.gitea/workflows/build.yml

@@ -26,8 +26,12 @@ jobs:
     # PGDATA: the timescaledb-ha image initialises at /home/postgres/pgdata/data;
     # the healthcheck uses pg_isready, which doesn't depend on the PGDATA path.
     #
-    # Port mapping: 5432:5432 binds the service on the runner's loopback.
-    # The dry-run docker run uses --network host so DB_HOST=localhost reaches it.
+    # Port mapping: 15432:5432 — host port 15432 is the conventional
+    # Postgres-second-instance port. We deliberately do NOT use 5432 on the
+    # runner because the runner host typically has another Postgres on 5432
+    # (dev stack, stage instance) which would cause a port-allocation collision.
+    # The dry-run docker run uses --network host so DB_HOST=localhost reaches
+    # the service on the runner's loopback at port 15432.
     # ---------------------------------------------------------------------------
     services:
       postgres:
@@ -37,7 +41,7 @@ jobs:
           POSTGRES_PASSWORD: directus
           POSTGRES_DB: directus
         ports:
-          - '5432:5432'
+          - '15432:5432'
         options: >-
           --health-cmd "pg_isready -U directus -d directus"
           --health-interval 5s
@@ -93,7 +97,7 @@ jobs:
             --entrypoint bash \
             -e DB_CLIENT=pg \
             -e DB_HOST=localhost \
-            -e DB_PORT=5432 \
+            -e DB_PORT=15432 \
             -e DB_USER=directus \
             -e DB_PASSWORD=directus \
             -e DB_DATABASE=directus \