Add standalone hook entry points for context, new, save, summary, and worker

- Implemented context-hook.ts for handling session start events.
- Created new-hook.ts for user prompt submission events.
- Developed save-hook.ts for post tool use events.
- Added summary-hook.ts for handling stop events.
- Introduced worker.ts as a standalone background process for the SDK agent.
- Each hook reads input from stdin, processes it, and handles errors gracefully.

.claude-plugin/marketplace.json

@@ -0,0 +1,13 @@
+{
+  "name": "thedotmack",
+  "owner": {
+    "name": "Alex Newman"
+  },
+  "plugins": [
+    {
+      "name": "claude-mem",
+      "source": "./claude-mem",
+      "description": "Persistent memory system for Claude Code"
+    }
+  ]
+}