fix: add mempalace-mcp console entry point for pipx/uv compatibility

The MCP server config used `python -m mempalace.mcp_server` which fails
when mempalace is installed via pipx or uv, since the system python
cannot find the module in the isolated venv. Adding a `mempalace-mcp`
console_scripts entry point ensures the MCP server works regardless of
installation method (pip, pipx, uv, conda).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude-plugin/.mcp.json

@@ -1,9 +1,5 @@
 {
   "mempalace": {
-    "command": "python3",
-    "args": [
-      "-m",
-      "mempalace.mcp_server"
-    ]
+    "command": "mempalace-mcp"
   }
 }