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>

docker-compose.yml

@@ -79,6 +79,9 @@ services:
         aliases: [task-stream-mcp]
     environment:
       TASKSTREAM_API_URL: http://task-stream-api:3000
+      # Domains it answers on (protection against DNS rebinding): the one Dokploy gives it.
+      MCP_ALLOWED_HOSTS: ${MCP_ALLOWED_HOSTS:-mcp.taskstream.pireon.dev,localhost}
+      MCP_LOG_LEVEL: ${MCP_LOG_LEVEL:-warn}
     depends_on:
       api: { condition: service_healthy }
     restart: unless-stopped