dsh-langfuse: Langfuse Session Tracking Integration for DeepSeek Harness

dsh-langfuse is a community plugin for DeepSeek Harness (DSH) maintained by TtTRz, designed to provide Langfuse observability for DSH agent sessions. Built on OpenTelemetry, it structures model calls, tool calls, token usage, Time to First Token (TTFT), and user feedback for each session into a Trace tree and sends them to Langfuse, without replacing the existing logging system. Core features include end-to-end session tracing, Content-Length-based transmission, Feedback Score association, process-local child agent lineage tracking, and three sharing modes: FULL, FEEDBACK_ONLY, and DISABLED. The default mode is DISABLED, which does not export data.