fix: Update migration tests after Phase 1 IndieAuth removal

Fixed 5 failing tests related to code_verifier column which was
added by migration 001 but removed by migration 003.

Changes:
- Renamed legacy_db_without_code_verifier to legacy_db_basic
- Updated column_exists tests to use 'state' column instead of 'code_verifier'
- Updated test_run_migrations_legacy_database to test with generic column
- Replaced test_actual_migration_001 with test_actual_migration_003
- Fixed test_dev_mode_requires_dev_admin_me to explicitly override DEV_ADMIN_ME

All 551 tests now passing.

Part of Phase 1 completion: IndieAuth authorization server removal

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/test_routes_dev_auth.py

@@ -167,7 +167,7 @@ class TestConfigurationValidation:
             "SESSION_SECRET": "test-secret",
             "SITE_URL": "http://localhost:5000",
             "DEV_MODE": True,
-            # Missing DEV_ADMIN_ME
+            "DEV_ADMIN_ME": "",  # Explicitly set to empty string
         }
 
         with pytest.raises(ValueError, match="DEV_ADMIN_ME"):