feat(15-02): integrate KBSettings config for semantic segmentation

- Modified SRTProcessor to read enable_semantic_segmentation from KBSettings
- Changed constructor parameter default from False to None (None = read from config)
- Added config priority: constructor parameter > KBSettings > default (True)
- Added logging for config status (INFO level)
- Added comprehensive tests for config integration (TestConfigIntegration)
- Added tests for output format compatibility (TestOutputFormatBenefits)
- Fixed MockAIClient to accept disable_reasoning parameter
- All 34 tests passing

Requirements satisfied:
- CONFIG-01: SRTProcessor reads from KBSettings
- CONFIG-02: Disabled config uses rule-based segmentation
- OUTPUT-01: LLM segmentation outputs H2 titles
- OUTPUT-02: title=null skips title output
- OUTPUT-03: Rule-based segmentation outputs "## 内容"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

kb_workflow/pipeline/processors/srt.py

@@ -49,7 +49,7 @@ class SRTProcessor(BaseProcessor):
         self,
         state_manager: Optional[WorkflowStateManager] = None,
         enable_correction: bool = True,
-        enable_semantic_segmentation: bool = False,
+        enable_semantic_segmentation: Optional[bool] = None,
         enable_cache: bool = True
     ):
         """初始化 SRT 处理器
@@ -57,10 +57,24 @@ class SRTProcessor(BaseProcessor):
         Args:
             state_manager: 状态管理器
             enable_correction: 是否启用 ASR 纠错（默认 True）
-            enable_semantic_segmentation: 是否启用 LLM 语义分段（默认 False）
+            enable_semantic_segmentation: 是否启用 LLM 语义分段（None 时从配置读取）
             enable_cache: 是否启用缓存（默认 True，仅在启用语义分段时有效）
         """
         super().__init__(state_manager)
+
+        # 如果未明确指定，从配置读取
+        if enable_semantic_segmentation is None:
+            settings = get_settings()
+            enable_semantic_segmentation = settings.enable_semantic_segmentation
+            logger.info(
+                f"SRTProcessor using config: "
+                f"semantic_segmentation={'enabled' if enable_semantic_segmentation else 'disabled'}"
+            )
+        elif enable_semantic_segmentation:
+            logger.info("SRTProcessor using explicit parameter: semantic_segmentation=enabled")
+        else:
+            logger.info("SRTProcessor using explicit parameter: semantic_segmentation=disabled")
+
         self.enable_correction = enable_correction
         self.enable_semantic_segmentation = enable_semantic_segmentation
         self.segmenter = None