refactor(rag): extract retrieval and ingest to py-rag service

- replace in-process Milvus stack with PyRagClient + PyRagKnowledgeSearchAdapter behind KnowledgeSearchPort (RERANK score passthrough)
- move document ingest to py-rag /documents:ingest; DocumentManagementService keeps MySQL ledger + local files
- sink L0 query understanding to py-rag; drop KnowledgeQueryTransformer, single UNFILTERED_VECTOR attempt
- remove Milvus deps, config classes, dead demo services and obsolete rebuild scripts
- compose/Makefile reduced to MySQL/Redis; add pyrag.* config

pom.xml

@@ -76,12 +76,6 @@
             <artifactId>spring-ai-starter-model-deepseek</artifactId>
         </dependency>
 
-        <!-- Embedding: SiliconFlow BGE-M3 (需要 OpenAI 模块的 OpenAiEmbeddingModel) -->
-        <dependency>
-            <groupId>org.springframework.ai</groupId>
-            <artifactId>spring-ai-starter-model-openai</artifactId>
-        </dependency>
-
         <dependency>
             <groupId>com.alibaba.cloud.ai</groupId>
             <artifactId>spring-ai-alibaba-agent-framework</artifactId>
@@ -91,19 +85,14 @@
             <artifactId>spring-boot-starter-web</artifactId>
         </dependency>
         <!--
-          spring-boot-devtools removed on purpose.
-          Classpath restart (restartedMain) recreates beans without reliably closing
-          MilvusClientV2 gRPC channels, causing orphan channels and long hybrid RPC retries.
-          Prefer full process restart: stop then `mvn spring-boot:run`.
+          spring-boot-devtools removed on purpose (bean recreation on classpath restart
+          is unreliable). Prefer full process restart: stop then `mvn spring-boot:run`.
         -->
+        <!-- okhttp：DashScopeConfig 的 RestClient.Builder 使用（此前由 milvus-sdk 传递引入） -->
         <dependency>
-            <groupId>io.milvus</groupId>
-            <artifactId>milvus-sdk-java</artifactId>
-            <version>2.6.10</version>
-        </dependency>
-        <dependency>
-            <groupId>org.springframework.ai</groupId>
-            <artifactId>spring-ai-starter-vector-store-milvus</artifactId>
+            <groupId>com.squareup.okhttp3</groupId>
+            <artifactId>okhttp</artifactId>
+            <version>4.12.0</version>
         </dependency>
         <dependency>
             <groupId>org.springframework.boot</groupId>