Split database config into DATABASE_* components

Assemble the Postgres DSN from DATABASE_ENGINE/HOST/PORT/NAME/USER/
PASSWORD/OPTIONS so only the password needs to live in a secret; the
rest can go in a ConfigMap. DATABASE_URL remains a full-DSN override
(used by the sqlite test suite). Credentials are percent-encoded, the
port and options are omitted when empty, and the k8s migrate
initContainer now also reads the config ConfigMap.

server/.env.example

@@ -1,10 +1,17 @@
-# Postgres
-POSTGRES_HOST=localhost
-POSTGRES_PORT=5432
-POSTGRES_DB=tavolo
-POSTGRES_USER=tavolo
-POSTGRES_PASSWORD=tavolo
-DATABASE_URL=postgres://tavolo:tavolo@localhost:5432/tavolo
+# Database (match statistics). The app assembles the DSN from these
+# parts; DATABASE_PORT may be left unset to use the driver default
+# (5432 for Postgres). DATABASE_OPTIONS is a raw query string appended
+# to the URL (e.g. ssl=require); leave empty for none.
+DATABASE_ENGINE=postgres
+DATABASE_HOST=localhost
+DATABASE_PORT=5432
+DATABASE_NAME=tavolo
+DATABASE_USER=tavolo
+DATABASE_PASSWORD=password
+DATABASE_OPTIONS=
+# Full-DSN override: when set, the parts above are ignored. Used by the
+# test suite (sqlite://:memory:) and handy for managed-DB URLs.
+#DATABASE_URL=postgres://tavolo:password@localhost:5432/tavolo
 
 # OIDC (mock-oauth2-server in dev; it does not validate clients, so any
 # client id/secret works. For a real IdP like Keycloak, use its values here.)