refactor: remove test.db, use only posterg.db for all environments

- Simplified Database.php determineDatabasePath to always use posterg.db
- Removed test.db auto-detection based on php_sapi_name
- Removed test.db targets from justfile (migrate-test removed)
- Removed CreateTestDatabase.php fixture script
- Updated migrate.sh to only init posterg.db
- Updated setup-dev.sh to init posterg.db
- Updated run-tests.php (removed DB_ENV=test env var)
- Updated deploy-db to use posterg.db
- Removed test.db file

refactor: remove empty fixtures directory

scripts/migrate.sh

@@ -1,17 +1,14 @@
 #!/usr/bin/env bash
-# Initialise one or both SQLite databases from schema.sql.
+# Initialise the Post-ERG SQLite database from schema.sql.
 # Safe to run on existing databases — schema uses IF NOT EXISTS / INSERT OR IGNORE.
 # Usage:
-#   scripts/migrate.sh              # both test.db and posterg.db
-#   scripts/migrate.sh test         # storage/test.db only
-#   scripts/migrate.sh prod         # storage/posterg.db only
+#   scripts/migrate.sh              # posterg.db (default)
 
 set -euo pipefail
 
 REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
 APP_DIR="$REPO_ROOT/app"
 SCHEMA="$APP_DIR/storage/schema.sql"
-TEST_DB="$APP_DIR/storage/test.db"
 PROD_DB="$APP_DIR/storage/posterg.db"
 
 init_db() {
@@ -22,17 +19,4 @@ init_db() {
     echo "  [$label] done"
 }
 
-TARGET="${1:-both}"
-
-case "$TARGET" in
-    test)  init_db "$TEST_DB"  "test.db"    ;;
-    prod)  init_db "$PROD_DB"  "posterg.db" ;;
-    both)
-        init_db "$TEST_DB"  "test.db"
-        init_db "$PROD_DB"  "posterg.db"
-        ;;
-    *)
-        echo "Usage: $0 [test|prod|both]" >&2
-        exit 1
-        ;;
-esac
+init_db "$PROD_DB" "posterg.db"