[Studio] Validate proxy restart requests

[Aias00]

Summary

• validate proxy restart clusterId and addr before invoking cluster operations
• enable controller-level request validation for proxy restarts
• add controller tests for valid restart requests and invalid inputs

Scope

• RocketMQ Studio contest scope: Track 1 / ARCH-01 Proxy cluster management hardening
• Does not introduce Namespace behavior

Tests

• JAVA_HOME=/Users/aias/Library/Java/JavaVirtualMachines/openjdk-21.0.2/Contents/Home mvn -q -Dtest=ProxyControllerTest,ClusterServiceTest test
• JAVA_HOME=/Users/aias/Library/Java/JavaVirtualMachines/openjdk-21.0.2/Contents/Home mvn -q test
• git diff --check

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[Aias00]

Superseded by #633. Consolidated with related cluster operation validation changes to reduce review overhead while preserving the same scoped fixes and tests.