fix: correct wiki create endpoint and use strict undefined checks

- Change create endpoint from /wiki/new (web UI route) to /wiki/pages (API route)
- Use !== undefined instead of truthiness checks for optional string params

src/index.ts

@@ -1074,8 +1074,8 @@ server.tool(
 			title,
 			content_base64: Buffer.from(content).toString('base64'),
 		};
-		if (message) body.message = message;
-		return formatResponse(await clientFor(connection).post(`/repos/${owner}/${repo}/wiki/new`, body));
+		if (message !== undefined) body.message = message;
+		return formatResponse(await clientFor(connection).post(`/repos/${owner}/${repo}/wiki/pages`, body));
 	},
 );
 
@@ -1094,8 +1094,8 @@ server.tool(
 		const body: Record<string, unknown> = {
 			content_base64: Buffer.from(content).toString('base64'),
 		};
-		if (title) body.title = title;
-		if (message) body.message = message;
+		if (title !== undefined) body.title = title;
+		if (message !== undefined) body.message = message;
 		return formatResponse(await clientFor(connection).patch(`/repos/${owner}/${repo}/wiki/page/${page_name}`, body));
 	},
 );