feat: add NotificationsService with SSE subject pool

package-lock.json

@@ -51,6 +51,7 @@
         "@nestjs/common": "^11.0.1",
         "@nestjs/config": "^4.0.4",
         "@nestjs/core": "^11.0.1",
+        "@nestjs/event-emitter": "^3.1.0",
         "@nestjs/jwt": "^11.0.2",
         "@nestjs/passport": "^11.0.5",
         "@nestjs/platform-express": "^11.1.19",
@@ -2981,6 +2982,19 @@
         }
       }
     },
+    "node_modules/@nestjs/event-emitter": {
+      "version": "3.1.0",
+      "resolved": "https://registry.npmmirror.com/@nestjs/event-emitter/-/event-emitter-3.1.0.tgz",
+      "integrity": "sha512-DOY/4XBGyIjYyOJKkO6jl1kzFE0ZfX0wV+M2HR5NWymPT9Z0zdCEcZGxTXXkoMRwPtglnvCGJALSjOpXPIcM3g==",
+      "license": "MIT",
+      "dependencies": {
+        "eventemitter2": "6.4.9"
+      },
+      "peerDependencies": {
+        "@nestjs/common": "^10.0.0 || ^11.0.0",
+        "@nestjs/core": "^10.0.0 || ^11.0.0"
+      }
+    },
     "node_modules/@nestjs/jwt": {
       "version": "11.0.2",
       "resolved": "https://registry.npmmirror.com/@nestjs/jwt/-/jwt-11.0.2.tgz",
@@ -8861,6 +8875,12 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/eventemitter2": {
+      "version": "6.4.9",
+      "resolved": "https://registry.npmmirror.com/eventemitter2/-/eventemitter2-6.4.9.tgz",
+      "integrity": "sha512-JEPTiaOt9f04oa6NOkc4aH+nVp5I3wEjpHbIPqfgCdD5v5bUzy7xQqwcVO2aDQgOWhI28da57HksMrzK9HlRxg==",
+      "license": "MIT"
+    },
     "node_modules/events": {
       "version": "3.3.0",
       "resolved": "https://registry.npmmirror.com/events/-/events-3.3.0.tgz",