feat: add Anthropic Claude Messages API client

Adds AnthropicClient with tool use, SSE streaming, and extended
thinking behind an optional AnthropicDialect bean, plus ANTHROPIC
model provider, request-shaping unit tests, and integration tests
against an Anthropic-compatible server.

src/test/resources/local-anthropic.properties

@@ -0,0 +1,16 @@
+category=ANTHROPIC
+prompts=
+tokenizer=fallback
+tokenEncoding=cl100k_base
+maxTokens=2500
+maxContextLength=180000
+temperature=0.3
+topP=0.95
+modelProvider=ANTHROPIC
+modelName=qwen3.8-flash-next-unsloth-ud-iq4_xs
+url=http://127.0.0.1:5001
+apiKey=test
+cost1MInTokens=0
+cost1MCachedInTokens=0
+cost1MOutTokens=0
+cost1MReasoningOutTokens=0