feat: notifications in the app and, optionally, by e-mail

Derived from events and kept per person: whoever a ticket is assigned to,
whoever reports or works on it when it moves, fails QA or gets a comment,
and whoever joins a project. Never about what you did yourself, once per
event. They arrive live through a subscription to a bell in the header,
and are copied by e-mail to whoever turns it on when SMTP_URL is set.

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

package-lock.json

@@ -49,6 +49,7 @@
         "ioredis": "^5.11.1",
         "joi": "^18.2.9",
         "mongoose": "^8.24.4",
+        "nodemailer": "^7.0.13",
         "openapi-fetch": "^0.17.0",
         "pg": "^8.23.1",
         "reflect-metadata": "^0.2.0",
@@ -91,6 +92,7 @@
         "@swc/helpers": "~0.5.18",
         "@types/jest": "~30.0.0",
         "@types/node": "^22.0.0",
+        "@types/nodemailer": "^8.0.2",
         "@types/ws": "^8.18.2",
         "@typescript-eslint/utils": "^8.58.0",
         "@vitest/coverage-v8": "~4.1.0",
@@ -14354,6 +14356,16 @@
         "undici-types": "~6.21.0"
       }
     },
+    "node_modules/@types/nodemailer": {
+      "version": "8.0.2",
+      "resolved": "https://registry.npmjs.org/@types/nodemailer/-/nodemailer-8.0.2.tgz",
+      "integrity": "sha512-c7M5ox8p0nEOfbJ2E9Qcmt8/QCu/VzsiAhzBiZbvky2PhKZDHpKB3sQHBM5MEZNkCfBOaS6S9//AGPRTNB7IaA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/parse-json": {
       "version": "4.0.2",
       "devOptional": true,
@@ -25205,6 +25217,15 @@
         "node": ">=18"
       }
     },
+    "node_modules/nodemailer": {
+      "version": "7.0.13",
+      "resolved": "https://registry.npmjs.org/nodemailer/-/nodemailer-7.0.13.tgz",
+      "integrity": "sha512-PNDFSJdP+KFgdsG3ZzMXCgquO7I6McjY2vlqILjtJd0hy8wEvtugS9xKRF2NWlPNGxvLCXlTNIae4serI7dinw==",
+      "license": "MIT-0",
+      "engines": {
+        "node": ">=6.0.0"
+      }
+    },
     "node_modules/normalize-path": {
       "version": "3.0.0",
       "license": "MIT",