test(server): add Sonnet 4.6 1M to claude-agent listModels expectation

PR #799 added claude-sonnet-4-6[1m] to the model catalog and updated
claude-models.test.ts but missed the duplicate assertion in
claude-agent.test.ts.

packages/server/src/server/agent/providers/claude-agent.test.ts

@@ -354,6 +354,7 @@ describe("ClaudeAgentClient.listModels", () => {
       "claude-opus-4-7",
       "claude-opus-4-6[1m]",
       "claude-opus-4-6",
+      "claude-sonnet-4-6[1m]",
       "claude-sonnet-4-6",
       "claude-haiku-4-5",
     ]);