fix(backend): switch to sentry-spring-boot-4:8.41.0 for Spring Boot 4/SF7 compatibility

sentry-spring-boot-starter-jakarta 8.5.0 does not support Spring Boot 4.0 —
it logs an "Incompatible Spring Boot Version" warning and its SentryAutoConfiguration
crashes SF7 bean-name generation. sentry-spring-boot-4 (added in 8.21.0) is the
dedicated Spring Boot 4 module with a fixed auto-configuration class.

- Replace sentry-spring-boot-starter-jakarta:8.5.0 with sentry-spring-boot-4:8.41.0
- Delete SentryConfig.java — workaround no longer needed, auto-config handles init
- Remove spring.autoconfigure.exclude from application.yaml + application-test.yaml
- Delete SentryConfigTest.java — tested the deleted workaround class
- Update ApplicationContextTest: assert Sentry.isEnabled() is false when no DSN set

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/pom.xml

@@ -225,11 +225,13 @@
 			</exclusions>
 		</dependency>
 
-		<!-- Sentry error reporting (GlitchTip-compatible) -->
+		<!-- Sentry error reporting (GlitchTip-compatible) — sentry-spring-boot-4 is the
+		     Spring Boot 4 / Spring Framework 7 compatible module (replaces the jakarta starter
+		     which crashes with SF7 due to bean-name generation for triply-nested @Import classes) -->
 		<dependency>
 			<groupId>io.sentry</groupId>
-			<artifactId>sentry-spring-boot-starter-jakarta</artifactId>
-			<version>8.5.0</version>
+			<artifactId>sentry-spring-boot-4</artifactId>
+			<version>8.41.0</version>
 		</dependency>
 	</dependencies>