Split API and frontend, migrate SQLite to PostgreSQL

- api.fahrschultermin.de: full API entry point with CORS + session auth
- fahrschultermin.de: frontend only, no more /api/v1 routing
- Database.php: PostgreSQL support (pgsql driver + lastval())
- All repositories: use Database::lastInsertId() for PG compatibility
- config/app.php: PostgreSQL connection settings + CORS config
- bootstrap.php: pass full $config to Database::configure()
- public/index.php: fetch-patch to redirect /api/v1 to api.fahrschultermin.de
- database/schema_pgsql.sql: full PostgreSQL schema (BIGSERIAL)
- database/import_pgsql.sql: 518 rows migrated from SQLite

www/fahrschultermin.de/app/Repositories/AppointmentRepository.php

@@ -84,7 +84,7 @@ final class AppointmentRepository extends BaseRepository
             'updated_at' => $timestamp,
         ]);
 
-        $appointmentId = (int) $this->db->lastInsertId();
+        $appointmentId = (int) $this->lastInsertId();
         $this->replaceUnits($appointmentId, $data['units_breakdown'] ?? []);
 
         return $this->find($tenantId, $appointmentId);

www/fahrschultermin.de/app/Repositories/BaseRepository.php

@@ -16,6 +16,11 @@ abstract class BaseRepository
         $this->db = Database::connection();
     }
 
+    protected function lastInsertId(): string
+    {
+        return Database::lastInsertId();
+    }
+
     protected function now(): string
     {
         return gmdate('c');

www/fahrschultermin.de/app/Repositories/InstructorRepository.php

@@ -45,7 +45,7 @@ final class InstructorRepository extends BaseRepository
             'updated_at' => $timestamp,
         ]);
 
-        return $this->find($tenantId, (int) $this->db->lastInsertId());
+        return $this->find($tenantId, (int) $this->lastInsertId());
     }
 
     public function update(int $tenantId, int $id, array $data): ?array

www/fahrschultermin.de/app/Repositories/ReferenceDataRepository.php

@@ -66,7 +66,7 @@ final class ReferenceDataRepository extends BaseRepository
             'created_at' => $timestamp,
             'updated_at' => $timestamp,
         ]);
-        $lessonTypeId = (int) $this->db->lastInsertId();
+        $lessonTypeId = (int) $this->lastInsertId();
         $this->replaceLessonTypeVisibility($tenantId, $lessonTypeId, $data['visible_template_ids'] ?? null);
 
         return $this->findLessonType($tenantId, $lessonTypeId);
@@ -225,7 +225,7 @@ final class ReferenceDataRepository extends BaseRepository
             'created_at' => $timestamp,
             'updated_at' => $timestamp,
         ]);
-        $templateId = (int) $this->db->lastInsertId();
+        $templateId = (int) $this->lastInsertId();
 
         $this->replaceTemplateRequirements($templateId, $data['requirements'] ?? []);
         $this->attachTemplateToExistingStudentLessonTypes($tenantId, $templateId);

www/fahrschultermin.de/app/Repositories/StudentRepository.php

@@ -60,7 +60,7 @@ final class StudentRepository extends BaseRepository
             'updated_at' => $timestamp,
         ]);
 
-        $studentId = (int) $this->db->lastInsertId();
+        $studentId = (int) $this->lastInsertId();
         $this->snapshotRequirements($studentId, (int) $data['template_id']);
 
         return $this->find($tenantId, $studentId);

www/fahrschultermin.de/app/Repositories/TenantRepository.php

@@ -40,7 +40,7 @@ final class TenantRepository extends BaseRepository
             'updated_at' => $timestamp,
         ]);
 
-        return $this->find((int) $this->db->lastInsertId());
+        return $this->find((int) $this->lastInsertId());
     }
 
     public function update(int $id, array $data): ?array

www/fahrschultermin.de/app/Repositories/UserRepository.php

@@ -74,7 +74,7 @@ final class UserRepository extends BaseRepository
             'updated_at' => $timestamp,
         ]);
 
-        return $this->findById((int) $this->db->lastInsertId());
+        return $this->findById((int) $this->lastInsertId());
     }
 
     public function update(int $id, array $data): ?array