refactor: consolidate stream smoothing into StreamProcessor with intelligent timing

- Move StreamSmoother functionality directly into StreamProcessor for better integration
- Create ContentExtractor strategy pattern for format-agnostic content extraction
- Implement intelligent dynamic delay calculation based on text length
- Support three text length tiers: short (char-by-char), medium (chunked), long (chunked)
- Remove manual chunk_size and delay_ms configuration - now auto-calculated
- Simplify admin UI to single toggle switch with auto timing adjustment
- Extract format detection logic to reusable content_extractors module
- Improve code maintainability with cleaner architecture

src/api/handlers/base/chat_handler_base.py

@@ -298,16 +298,11 @@ class ChatHandlerBase(BaseMessageHandler, ABC):
         def update_streaming_status() -> None:
             self._update_usage_to_streaming_with_ctx(ctx)
 
-        # 从数据库批量读取流式平滑输出配置（单次查询）
-        smoothing_cfg = SystemConfigService.get_configs(
-            self.db,
-            ["stream_smoothing_enabled", "stream_smoothing_chunk_size", "stream_smoothing_delay_ms"],
-        )
-        smoothing_config = StreamSmoothingConfig(
-            enabled=bool(smoothing_cfg.get("stream_smoothing_enabled", False)),
-            chunk_size=int(smoothing_cfg.get("stream_smoothing_chunk_size") or 5),
-            delay_ms=int(smoothing_cfg.get("stream_smoothing_delay_ms") or 15),
+        # 读取流式平滑输出开关
+        smoothing_enabled = bool(
+            SystemConfigService.get_config(self.db, "stream_smoothing_enabled", False)
         )
+        smoothing_config = StreamSmoothingConfig(enabled=smoothing_enabled)
 
         # 创建流处理器
         stream_processor = StreamProcessor(