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

app/src/Database.php

@@ -35,7 +35,7 @@ class Database {
 
     /**
      * Determine database path.
-     * Priority: explicit override → DB_ENV env-var → sapi auto-detect.
+     * Priority: explicit override → APP_ROOT /storage/posterg.db.
      * APP_ROOT is defined by bootstrap.php before any controller loads Database.
      */
     private function determineDatabasePath($customPath = null): string {
@@ -44,15 +44,7 @@ class Database {
         }
 
         $root    = defined('APP_ROOT') ? APP_ROOT : __DIR__ . '/..';
-        $testDb  = $root . '/storage/test.db';
-        $prodDb  = $root . '/storage/posterg.db';
-
-        $env = getenv('DB_ENV');
-        if ($env === 'test') return $testDb;
-        if ($env === 'prod') return $prodDb;
-
-        // php -S (dev server) → test DB; everything else (nginx/fpm) → prod DB
-        return php_sapi_name() === 'cli-server' ? $testDb : $prodDb;
+        return $root . '/storage/posterg.db';
     }
 
     /**