Keep the engine's state in SQLite, not Postgres

One process owns this database — the image has run a single uvicorn
worker for that reason since the four-engines bug — so a file beside the
flows is the honest shape for it, and it is what lets `fluksio serve`
need no infrastructure at all. Live values, node execution and the work
queue never came here anyway; what does is a rollup a minute at a time,
a row per cascade and the run history, and WAL keeps the readers going
while that one writer works.

DATA_DIR is now the one setting that moves everything an installation
keeps; the rest derive from it and the images still spell theirs out.
The schema is prepared in-process at startup, so the prestart service is
gone, and the ten Postgres-only revisions collapse into one portable
baseline.

Three things only worked because psycopg was casting for us: a token's
subject arriving as a string where the column is a UUID, `greatest`, and
`date_bin`. The timestamps needed a column type of their own — SQLite
stores no offset, and a naive datetime read back either raises against an
aware `now` or serialises as local time.

Postgres stays in the stack only for Umami, behind the analytics profile.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docker/compose.yml

@@ -7,14 +7,17 @@
 
 services:
 
+  # Umami's database, and nothing else's. The engine keeps its own state in
+  # SQLite on the flow-data volume, which is why this is behind a profile now.
   db:
     image: postgres:18
     container_name: fluksio-db
     restart: always
+    profiles: ["analytics"]
     security_opt:
       - no-new-privileges:true
     healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-postgres} -d ${POSTGRES_DB:-app}"]
       interval: 10s
       retries: 5
       start_period: 30s
@@ -25,9 +28,11 @@ services:
       - ../.env
     environment:
       - PGDATA=/var/lib/postgresql/data/pgdata
-      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD?Variable not set}
-      - POSTGRES_USER=${POSTGRES_USER?Variable not set}
-      - POSTGRES_DB=${POSTGRES_DB?Variable not set}
+      # Not required of the stack at large any more: only the analytics
+      # profile starts this, and the engine has no Postgres to configure.
+      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD:-postgres}
+      - POSTGRES_USER=${POSTGRES_USER:-postgres}
+      - POSTGRES_DB=${POSTGRES_DB:-app}
 
   redis:
     image: redis:8.2-alpine
@@ -54,6 +59,7 @@ services:
     image: adminer
     container_name: fluksio-adminer
     restart: always
+    profiles: ["analytics"]
     security_opt:
       - no-new-privileges:true
     # Deliberately not on `proxy`: the Postgres UI is reachable from the host
@@ -65,43 +71,6 @@ services:
     environment:
       - ADMINER_DESIGN=pepa-linha-dark
 
-  prestart:
-    image: '${DOCKER_IMAGE_BACKEND?Variable not set}:${TAG-latest}'
-    container_name: fluksio-prestart
-    build:
-      context: ..
-      dockerfile: backend/Dockerfile
-    security_opt:
-      - no-new-privileges:true
-    networks:
-      - proxy
-      - default
-    depends_on:
-      db:
-        condition: service_healthy
-        restart: true
-    command: bash scripts/prestart.sh
-    env_file:
-      - ../.env
-    environment:
-      - DOMAIN=${DOMAIN}
-      - FRONTEND_HOST=${FRONTEND_HOST?Variable not set}
-      - ENVIRONMENT=${ENVIRONMENT}
-      - BACKEND_CORS_ORIGINS=${BACKEND_CORS_ORIGINS}
-      - SECRET_KEY=${SECRET_KEY?Variable not set}
-      - FIRST_SUPERUSER=${FIRST_SUPERUSER?Variable not set}
-      - FIRST_SUPERUSER_PASSWORD=${FIRST_SUPERUSER_PASSWORD?Variable not set}
-      - SMTP_HOST=${SMTP_HOST}
-      - SMTP_USER=${SMTP_USER}
-      - SMTP_PASSWORD=${SMTP_PASSWORD}
-      - EMAILS_FROM_EMAIL=${EMAILS_FROM_EMAIL}
-      - POSTGRES_SERVER=db
-      - POSTGRES_PORT=${POSTGRES_PORT}
-      - POSTGRES_DB=${POSTGRES_DB}
-      - POSTGRES_USER=${POSTGRES_USER?Variable not set}
-      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD?Variable not set}
-      - SENTRY_DSN=${SENTRY_DSN}
-
   backend:
     image: '${DOCKER_IMAGE_BACKEND?Variable not set}:${TAG-latest}'
     container_name: fluksio-api
@@ -112,14 +81,9 @@ services:
       - proxy
       - default
     depends_on:
-      db:
-        condition: service_healthy
-        restart: true
       redis:
         condition: service_healthy
         restart: true
-      prestart:
-        condition: service_completed_successfully
     env_file:
       - ../.env
     environment:
@@ -134,14 +98,13 @@ services:
       - SMTP_USER=${SMTP_USER}
       - SMTP_PASSWORD=${SMTP_PASSWORD}
       - EMAILS_FROM_EMAIL=${EMAILS_FROM_EMAIL}
-      - POSTGRES_SERVER=db
-      - POSTGRES_PORT=${POSTGRES_PORT}
-      - POSTGRES_DB=${POSTGRES_DB}
-      - POSTGRES_USER=${POSTGRES_USER?Variable not set}
-      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD?Variable not set}
       - SENTRY_DSN=${SENTRY_DSN}
       # Flow state survives a restart in Redis; without a host it stays in memory.
       - REDIS_HOST=redis
+      # Everything this installation keeps — the database, the flows, secrets,
+      # artifacts and the user venv — on one volume. The paths below derive
+      # from it; they are spelled out because each is load bearing.
+      - DATA_DIR=/data
       # Flows are files in a git repository; secrets sit encrypted beside it.
       - FLOWS_DIR=/data/flows
       - SECRETS_FILE=/data/secrets.enc