fix(obs): set POSTGRES_HOST per environment — staging/prod use compose auto-names not archive-db

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/nightly.yml

@@ -144,6 +144,7 @@ jobs:
           GLITCHTIP_SECRET_KEY=${{ secrets.GLITCHTIP_SECRET_KEY }}
           POSTGRES_USER=archiv
           POSTGRES_PASSWORD=${{ secrets.STAGING_POSTGRES_PASSWORD }}
+          POSTGRES_HOST=archiv-staging-db-1
           EOF
 
       - name: Validate observability compose config

.gitea/workflows/release.yml

@@ -112,6 +112,7 @@ jobs:
           GLITCHTIP_SECRET_KEY=${{ secrets.GLITCHTIP_SECRET_KEY }}
           POSTGRES_USER=archiv
           POSTGRES_PASSWORD=${{ secrets.PROD_POSTGRES_PASSWORD }}
+          POSTGRES_HOST=archiv-production-db-1
           EOF
 
       - name: Start observability stack

infra/observability/obs.env

@@ -15,6 +15,8 @@ GF_SERVER_ROOT_URL=https://grafana.archiv.raddatz.cloud
 GLITCHTIP_DOMAIN=https://glitchtip.archiv.raddatz.cloud
 
 # PostgreSQL hostname for GlitchTip db-init and workers.
-# archive-db is the production default (full stack running).
-# Override in obs-secrets.env when a different stack is active.
-POSTGRES_HOST=archive-db
+# The actual value depends on the Compose project name — it is not a fixed string.
+# CI sets POSTGRES_HOST in obs-secrets.env per environment:
+#   staging:    archiv-staging-db-1    (project archiv-staging + service db)
+#   production: archiv-production-db-1 (project archiv-production + service db)
+# For local dev, set POSTGRES_HOST in your .env file (defaults to archive-db there).