ci(test): reach the postgres service via service name, not 127.0.0.1

Now that BB1's port 5432 is freed, CI gets past the port-bind step
and actually attempts to run the tests. The next failure is:

  psycopg.OperationalError: connection to server at "127.0.0.1",
  port 5432 failed: Connection refused

The job tried 127.0.0.1:5432 but the postgres service container had
just been brought up and wasn't accepting connections yet. The
'5432:5432' port mapping for self-hosted act_runner is racy — the
host-side bind sometimes lags the service ready signal, and the
job's 'Apply schema' step runs before pg_isready returns 0.

Fix:
- Use the service name 'postgres' as DAMASCUS_PG_HOST. In act_runner's
  service network, the service name is the DNS hostname, no port
  mapping required.
- Drop the now-unused 'ports: 5432:5432' binding.

This is the same fix the cron branch fix/compose-db-volume-self-heal
should land in (PR #7). It's small enough to be a follow-up to this
PR; if the test workflow on BB1's runner doesn't resolve 'postgres',
we can revisit.

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

.gitea/workflows/test.yml

@@ -17,8 +17,6 @@ jobs:
           POSTGRES_USER: damascus
           POSTGRES_PASSWORD: damascus
           POSTGRES_DB: damascus
-        ports:
-          - "5432:5432"
         options: >-
           --health-cmd "pg_isready -U damascus -d damascus"
           --health-interval 5s
@@ -28,7 +26,12 @@ jobs:
     env:
       DAMASCUS_ROOT: ${{ github.workspace }}
       DAMASCUS_SCHEMA_PATH: ${{ github.workspace }}/schema.sql
-      DAMASCUS_PG_HOST: 127.0.0.1
+      # The postgres service is reachable by its service name on the runner
+      # network. We tried 127.0.0.1 + a host port binding first; the binding
+      # is racy on self-hosted act_runner (the port map sometimes takes
+      # effect after the job tries to connect, causing "Connection refused").
+      # Service-name DNS is reliable.
+      DAMASCUS_PG_HOST: postgres
       DAMASCUS_PG_PORT: "5432"
       DAMASCUS_PG_USER: damascus
       DAMASCUS_PG_PASSWORD: damascus