Add MCP server (stdio + HTTP) reusing the skill's Graph client

New mcp-server/ exposes SharePoint Lists as MCP tools (test, list_lists, get_columns, list_items, get_item, create/update/delete_item) via the same graph.mjs core. Supports stdio (Claude Desktop/Code/Cowork) and Streamable HTTP (--http). SP_READONLY gates write tools. Adds project .mcp.json and ignores build artifacts. Verified end-to-end live over stdio and HTTP initialize.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -8,6 +8,10 @@
 node_modules/
 npm-debug.log*
 
+# --- Packaged skill build artifacts ---
+*.zip
+*.skill
+
 # --- OS / editor cruft ---
 .DS_Store
 *.swp