fix: apply all A-J improvements across MCP server

- A: fix get_user_profile URL (/api/user/profile → /api/users/:username)
- B: fix unban_user to use DELETE /api/mod/users/:id/ban (was POST .../unban)
- C: add check_duplicates tool (GET /api/news/:id/check-duplicates)
- D: add shadowban_user tool (PATCH /api/mod/users/:id/shadowban)
- E: add create_mod_user tool (POST /api/mod/users)
- F: extract handleTool helper in utils.ts; all 37 tools now use it for
     consistent isError:true error responses visible to the AI model
- G: only send Content-Type header when request has a body
- H: support BETTERNEWS_BASE_URL env var for local dev overrides
- I: fix get_news_item_stats description (accessible by own author, not Mod/Admin only)
- J: add .describe() to page/limit/status params in list_all_tickets and list_my_tickets

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/index.ts

@@ -19,7 +19,8 @@ if (!apiKey) {
     process.exit(1);
 }
 
-const client = new BetterNewsClient(apiKey);
+const baseUrl = process.env.BETTERNEWS_BASE_URL ?? "https://api.betternews.app";
+const client = new BetterNewsClient(apiKey, baseUrl);
 
 const server = new McpServer({
     name: "betternews",