fix(config): auto-route test.db locally, posterg.db on production

- config.php: getDatabasePath() detects php built-in CLI server
  (php_sapi_name() === 'cli-server') and routes to test.db; all
  other SAPIs (nginx/fpm) get posterg.db. DB_ENV env-var still
  overrides either way.

- migrate.sh: auto-initialise the target DB from storage/schema.sql
  when the file is absent or has no tables yet. Existing DBs with
  data are left completely untouched (table_count check, no re-run
  of schema on populated DB). Idempotent: safe to run repeatedly.

- justfile: serve still calls migrate (which now handles init too),
  no DB_ENV prefix needed since sapi detection handles routing.

scripts/migrate.sh

@@ -63,9 +63,13 @@ migrate_db() {
     local db="$1"
     local label="$2"
 
-    if [ ! -f "$db" ]; then
-        echo "  [$label] database not found, skipping: $db"
-        return
+    # Auto-create from schema only when the file is absent or truly empty (no tables)
+    local table_count
+    table_count=$(sqlite3 "$db" "SELECT COUNT(*) FROM sqlite_master WHERE type='table';" 2>/dev/null || echo 0)
+    if [ "$table_count" -eq 0 ]; then
+        echo "  [$label] initialising from schema…"
+        sqlite3 "$db" < "$REPO_ROOT/storage/schema.sql"
+        echo "  [$label] schema applied."
     fi
 
     # Ensure tracking table exists