Add comprehensive documentation and templates for LangChain skill development

- Introduced a new reference document for streaming output issues, detailing the differences between streaming APIs and providing solutions for common problems.
- Created a structured output issues reference, outlining the use of `with_structured_output`, `response_format`, and schema enforcement strategies.
- Added a user query convention guide to standardize structured questions for skill authors, including block types for queries and data gathering.
- Implemented a template for a chat model, encapsulating API key management, request payload construction, and response handling.
- Established a symlink for the LangChain dev guide in the Claude skills directory for easier access.
- Initialized a skills lock file to manage dependencies and versions for the LangChain dev guide.

skills-lock.json

@@ -0,0 +1,11 @@
+{
+  "version": 1,
+  "skills": {
+    "langchain-dev-guide": {
+      "source": "ob-labs/agentseek",
+      "sourceType": "github",
+      "skillPath": "skills/langchain-dev-guide/SKILL.md",
+      "computedHash": "5772776e13375f078d3743c0899a28ffeb20bc6e9f7884e3b6e9d3826b0f6abc"
+    }
+  }
+}