fix: handle RateLimitBlockedException in ExceptionHandlers (#3472)

## Summary

- Add missing `@ExceptionHandler` for `RateLimitBlockedException` in
`ExceptionHandlers.kt`
- Returns HTTP 444 (no body), matching the existing behavior in
`GlobalIpRateLimitFilter` and `GlobalUserRateLimitFilter`

## Problem

The strike-based rate limiting (#3451, commit 68b5250) introduced
`RateLimitBlockedException` but only caught it in the global servlet
filters. When thrown from controller-level rate limiting (e.g. the
export endpoint's `checkPerUserRateLimit`), it bubbled up as an
unhandled exception — causing HTTP 500 errors and Sentry noise since Feb
6th.

## Test plan

- [ ] Verify export endpoint returns 444 instead of 500 for repeat rate
limit offenders
- [ ] Confirm no new Sentry errors for `RateLimitBlockedException`

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Improved handling of blocked rate-limit events so users receive a
clear status when limits are exceeded and related occurrences are logged
for better observability.

* **Tests**
* Made NDJSON error extraction in tests more resilient by scanning for
error messages instead of relying on a fixed position.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: dkrizan

backend/app/src/main/kotlin/io/tolgee/ExceptionHandlers.kt

@@ -12,6 +12,7 @@ import io.tolgee.exceptions.ErrorException
 import io.tolgee.exceptions.ErrorResponseBody
 import io.tolgee.exceptions.ErrorResponseTyped
 import io.tolgee.exceptions.NotFoundException
+import io.tolgee.security.ratelimit.RateLimitBlockedException
 import io.tolgee.security.ratelimit.RateLimitResponseBody
 import io.tolgee.security.ratelimit.RateLimitedException
 import io.tolgee.util.Logging
@@ -256,6 +257,12 @@ class ExceptionHandlers : Logging {
     )
   }
 
+  @ExceptionHandler(RateLimitBlockedException::class)
+  fun handleRateLimitBlocked(ex: RateLimitBlockedException): ResponseEntity<Unit> {
+    logger.debug("Rate limit blocked (strike {})", ex.strikeCount)
+    return ResponseEntity.status(444).build()
+  }
+
   @ExceptionHandler(NoResourceFoundException::class)
   fun handleNoResourceFound(ex: NoResourceFoundException): ResponseEntity<ErrorResponseBody> {
     logger.debug("No resource found", ex)

ee/backend/tests/src/test/kotlin/io/tolgee/ee/selfHostedLimitsAndReporting/CreditLimitTest.kt

@@ -107,7 +107,13 @@ class CreditLimitTest : ProjectAuthControllerTest("/v2/projects/") {
       }
     val parsed = NdJsonParser(objectMapper).parse(response)
     parsed.assert.hasSize(3)
-    (parsed[1] as Map<*, *>)["errorMessage"].assert.isEqualTo(errorCode)
+    val errorMessage =
+      parsed
+        .drop(1)
+        .filterIsInstance<Map<*, *>>()
+        .mapNotNull { it["errorMessage"] }
+        .firstOrNull()
+    errorMessage.assert.isEqualTo(errorCode)
   }
 
   private fun mockBadRequest(errorCode: String): HttpClientErrorException {