fix: revert unlimited check to < 0 — zero is a real limit

limit.limit is always set explicitly (never relies on the JPA default),
so 0 means a genuine strict-zero limit rather than "unlimited". Only
negative values (-1) represent unlimited. Update tests accordingly:
zero-limit cases now assert that an exception is thrown rather than
that the check is skipped.

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

Author: dkrizan

ee/backend/app/src/main/kotlin/io/tolgee/ee/component/limitsAndReporting/generic/GenericLimitChecker.kt

@@ -17,7 +17,7 @@ open class GenericLimitChecker(
   fun check(required: Long?) = check { required }
 
   fun check(requiredProvider: () -> Long?) {
-    if (limit.limit <= 0) {
+    if (limit.limit < 0) {
       return
     }
 

ee/backend/tests/src/test/kotlin/io/tolgee/ee/unit/limitsAndReporting/GenericLimitCheckerTest.kt

@@ -30,19 +30,12 @@ class GenericLimitCheckerTest {
   )
 
   @Test
-  fun `zero limit - no exception and provider not called`() {
-    var providerCalled = false
-    val checker =
-      checker(
-        zeroLimit(),
-        includedProvider = {
-          providerCalled = true
-          RuntimeException()
-        },
-      )
+  fun `zero limit - throws included exception (not treated as unlimited)`() {
+    val checker = checker(zeroLimit())
 
-    assertDoesNotThrow { checker.check { 999L } }
-    assertFalse(providerCalled)
+    val ex = assertThrows<RuntimeException> { checker.check { 999L } }
+
+    assert(ex.message == "included: 999")
   }
 
   @Test

ee/backend/tests/src/test/kotlin/io/tolgee/ee/unit/limitsAndReporting/KeysLimitCheckerTest.kt

@@ -5,7 +5,6 @@ import io.tolgee.ee.component.limitsAndReporting.generic.KeysLimitChecker
 import io.tolgee.exceptions.limits.PlanLimitExceededKeysException
 import io.tolgee.exceptions.limits.PlanSpendingLimitExceededKeysException
 import org.assertj.core.api.Assertions.assertThat
-import org.junit.jupiter.api.Assertions.assertDoesNotThrow
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertThrows
 
@@ -25,9 +24,10 @@ class KeysLimitCheckerTest {
   )
 
   @Test
-  fun `zero keys limit - no exception (unlimited detection bug fix)`() {
+  fun `zero keys limit - throws PlanLimitExceededKeysException (zero is a real limit)`() {
     val checker = KeysLimitChecker(usageLimits(keys = UsageLimits.Limit(included = 0, limit = 0)))
-    assertDoesNotThrow { checker.check { 999L } }
+
+    assertThrows<PlanLimitExceededKeysException> { checker.check { 999L } }
   }
 
   @Test

ee/backend/tests/src/test/kotlin/io/tolgee/ee/unit/limitsAndReporting/StringsLimitCheckerTest.kt

@@ -5,7 +5,6 @@ import io.tolgee.ee.component.limitsAndReporting.generic.StringsLimitChecker
 import io.tolgee.exceptions.limits.PlanLimitExceededStringsException
 import io.tolgee.exceptions.limits.PlanSpendingLimitExceededStringsException
 import org.assertj.core.api.Assertions.assertThat
-import org.junit.jupiter.api.Assertions.assertDoesNotThrow
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertThrows
 
@@ -25,9 +24,10 @@ class StringsLimitCheckerTest {
   )
 
   @Test
-  fun `zero strings limit - no exception (unlimited detection bug fix)`() {
+  fun `zero strings limit - throws PlanLimitExceededStringsException (zero is a real limit)`() {
     val checker = StringsLimitChecker(usageLimits(strings = UsageLimits.Limit(included = 0, limit = 0)))
-    assertDoesNotThrow { checker.check { 999L } }
+
+    assertThrows<PlanLimitExceededStringsException> { checker.check { 999L } }
   }
 
   @Test