fix(tool): make active tool groups concurrency-safe

[Alexxigang]

Summary

• store active tool-group names in a concurrency-safe snapshot set instead of a plain ArrayList
• keep ToolGroup.active aligned with setActiveGroups(...) replacements and concurrent updates
• add regression coverage for concurrent read/write access, snapshot replacement, and copyTo(...) isolation

Why this fix

ToolGroupManager already uses concurrent maps for group and tool indexes, but �ctiveGroups remained a mutable ArrayList. In concurrent agent scenarios, activation/deactivation and snapshot reads such as getActiveGroups() / getActivatedNotes() can race, and the list can diverge from each ToolGroup's active flag. This patch makes the active-group snapshot safe for concurrent access while preserving the existing public API.

Validation

• mvn -pl agentscope-core spotless:apply
• mvn -pl agentscope-core '-Dtest=ToolGroupManagerTest,ToolGroupManagerConcurrencyTest,ToolkitTest,ToolGroupsE2ETest' test

Closes #1165.