feat(email): phase 6 — replace Resend with Brevo transactional email

Removes resend npm dependency. Adds lib/notifications/mailer.ts with a
raw-HTTP Brevo wrapper (sendEmail + sendPasswordResetEmail). All three
notification files updated to use the new wrapper.

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

package-lock.json

@@ -21,8 +21,7 @@
         "pdf-lib": "^1.17.1",
         "pg": "^8.22.0",
         "react": "^19.2.7",
-        "react-dom": "^19.2.7",
-        "resend": "^6.17.2"
+        "react-dom": "^19.2.7"
       },
       "devDependencies": {
         "@tailwindcss/postcss": "^4",
@@ -8797,12 +8796,6 @@
         "node": ">= 0.4"
       }
     },
-    "node_modules/postal-mime": {
-      "version": "2.7.4",
-      "resolved": "https://registry.npmjs.org/postal-mime/-/postal-mime-2.7.4.tgz",
-      "integrity": "sha512-0WdnFQYUrPGGTFu1uOqD2s7omwua8xaeYGdO6rb88oD5yJ/4pPHDA4sdWqfD8wQVfCny563n/HQS7zTFft+f/g==",
-      "license": "MIT-0"
-    },
     "node_modules/postcss": {
       "version": "8.5.16",
       "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.16.tgz",
@@ -9093,27 +9086,6 @@
       "dev": true,
       "license": "ISC"
     },
-    "node_modules/resend": {
-      "version": "6.17.2",
-      "resolved": "https://registry.npmjs.org/resend/-/resend-6.17.2.tgz",
-      "integrity": "sha512-hbaXEORFIFfT2Bh03NsA/akTTTKkD1hiuJ88ke64c5dWVV6DyoLxzFve3OiZqVOQ+JKLJ5uVkPR6hlUslpJFoA==",
-      "license": "MIT",
-      "dependencies": {
-        "postal-mime": "2.7.4",
-        "standardwebhooks": "1.0.0"
-      },
-      "engines": {
-        "node": ">=20"
-      },
-      "peerDependencies": {
-        "@react-email/render": "*"
-      },
-      "peerDependenciesMeta": {
-        "@react-email/render": {
-          "optional": true
-        }
-      }
-    },
     "node_modules/resolve": {
       "version": "2.0.0-next.7",
       "resolved": "https://registry.npmjs.org/resolve/-/resolve-2.0.0-next.7.tgz",