fix(qa-agent): Pin spring-ai to 2.0.0-M6 instead of SNAPSHOT

The samples/quality-assurance/ai-agent module was the only project
pinned to spring-ai 2.0.0-SNAPSHOT. The snapshot API drifted so that
OllamaChatModel.Builder.defaultOptions(OllamaChatOptions) no longer
existed, breaking test compilation. Because CI builds every module on
every PR, this failure surfaced on all open Dependabot PRs even though
none of them touch this module.

Pin to the stable 2.0.0-M6 milestone (matching the other 2.x apps) and
drop the now-unused Spring snapshots repository.

Author: Yuriy Bezsonov

samples/quality-assurance/ai-agent/pom.xml

@@ -28,7 +28,7 @@
 	</scm>
 	<properties>
 		<java.version>25</java.version>
-		<spring-ai.version>2.0.0-SNAPSHOT</spring-ai.version>
+		<spring-ai.version>2.0.0-M6</spring-ai.version>
 		<mcp-client-security.version>0.0.3</mcp-client-security.version>
 		<testcontainers.version>1.21.4</testcontainers.version>
 	</properties>
@@ -38,14 +38,6 @@
 			<name>Spring Milestones</name>
 			<url>https://repo.spring.io/milestone</url>
 		</repository>
-		<repository>
-			<id>spring-snapshots</id>
-			<name>Spring Snapshots</name>
-			<url>https://repo.spring.io/snapshot</url>
-			<snapshots>
-				<enabled>true</enabled>
-			</snapshots>
-		</repository>
 	</repositories>
 	<dependencyManagement>
 		<dependencies>