feat(mcp): ready for a remote server: quiet logs and allowed domains

- Logs default to warnings and errors (MCP_LOG_LEVEL): the library logged
  every tool on every request (~48 lines per call).
- DNS rebinding protection on /mcp, as the MCP spec asks of HTTP servers:
  the Host header must be in MCP_ALLOWED_HOSTS (default: localhost; compose
  default mcp.taskstream.pireon.dev,localhost) and a browser Origin, when
  present, too; otherwise 403 with a JSON-RPC error. Uses the official
  validators from @modelcontextprotocol/server.
- Test for allowed/foreign Host and Origin; .env.example, compose and
  docs/09-mcp.md document the variables; Word/PDF regenerated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/mcp/src/app/mcp-hosts.middleware.ts

@@ -0,0 +1,46 @@
+import { Injectable, NestMiddleware } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import {
+  localhostAllowedHostnames,
+  validateHostHeader,
+  validateOriginHeader,
+} from '@modelcontextprotocol/server';
+import type { NextFunction, Request, Response } from 'express';
+
+/**
+ * Protection against DNS rebinding on /mcp (what the MCP spec asks of HTTP
+ * servers): the Host header must be one of MCP_ALLOWED_HOSTS (default: only
+ * localhost), and a browser's Origin, when sent, too. AI clients calling from
+ * a server send no Origin, so they only need the right domain.
+ */
+@Injectable()
+export class McpHostsMiddleware implements NestMiddleware {
+  private readonly hosts: string[];
+
+  constructor(config: ConfigService) {
+    const configured = (config.get<string>('MCP_ALLOWED_HOSTS') ?? '')
+      .split(',')
+      .map((host) => host.trim().toLowerCase())
+      .filter(Boolean);
+    this.hosts = configured.length ? configured : localhostAllowedHostnames();
+  }
+
+  use(req: Request, res: Response, next: NextFunction): void {
+    const error = this.rejection(req);
+    if (!error) return next();
+    res.status(403).json({
+      jsonrpc: '2.0',
+      id: null,
+      error: { code: -32000, message: error },
+    });
+  }
+
+  /** Why the request is refused, or null when its Host (and Origin, if any) are allowed. */
+  private rejection(req: Request): string | null {
+    const host = validateHostHeader(req.headers.host, this.hosts);
+    if ('message' in host) return host.message;
+    if (!req.headers.origin) return null;
+    const origin = validateOriginHeader(req.headers.origin, this.hosts);
+    return 'message' in origin ? origin.message : null;
+  }
+}