feat: add OpenProse plugin skills

extensions/open-prose/skills/prose/examples/06-explain-codebase.prose

@@ -0,0 +1,17 @@
+# Explain Codebase
+# Progressive exploration of an unfamiliar codebase
+
+# Start with the big picture
+session "List all directories and key files in this repository. Provide a high-level map of the project structure."
+
+# Understand the entry point
+session "Find the main entry point of the application. Explain how the program starts and initializes."
+
+# Trace a key flow
+session "Trace through a typical user request from start to finish. Document the key functions and modules involved."
+
+# Document architecture
+session "Based on your exploration, write a brief architecture document explaining how the major components fit together."
+
+# Identify patterns
+session "What design patterns and conventions does this codebase use? Document any patterns future contributors should follow."