Fix manifest.json license field to Apache-2.0 (#182)

v0.9.3 (#172) で Apache-2.0 に切り替え済みだが、mcp-server/manifest.json の
license フィールドが MIT のまま残っていた。Apache-2.0 に修正。

Refs #181

Co-authored-by: liplus-lin-lay <liplus-lin-lay@users.noreply.github.com>

Author: liplus-lin-lay

mcp-server/manifest.json

@@ -16,7 +16,7 @@
   "homepage": "https://github.com/Liplus-Project/github-webhook-mcp",
   "documentation": "https://github.com/Liplus-Project/github-webhook-mcp#readme",
   "support": "https://github.com/Liplus-Project/github-webhook-mcp/discussions",
-  "license": "MIT",
+  "license": "Apache-2.0",
   "icon": "icon.png",
   "server": {
     "type": "node",