feat(memory): add memory extension with core functionality and tests

- Implemented MemoryStore class for managing concepts with YAML frontmatter.
- Added methods for creating, reading, updating, and deleting concepts.
- Introduced locking mechanism for concurrent access.
- Developed search and hinting capabilities for concept retrieval.
- Created tests for access control and store functionality.
- Added long-term memory skill documentation and operational guidelines.
- Included package.json and package-lock.json for dependency management.

extensions/memory/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "kimiko-memory-extension",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "test": "node --test test/*.test.mjs"
+  },
+  "dependencies": {
+    "yaml": "^2.8.1"
+  }
+}