Fix SMTP delivery, add password reset and user deletion

SMTP:
- Add connection/greeting/socket timeouts so a stalled Gmail
  connection no longer hangs sign-up
- Wrap sendMail in try/catch and fall back to logging the code
- Derive secure from port (465 implicit TLS vs 587 STARTTLS)
- Strip whitespace from the Gmail app password
- Document SMTP_HOST/SMTP_PORT in .env.example and environment.d.ts

Password reset (new):
- POST /(api)/auth/forgot-password emails a 6-digit code and does
  not reveal whether the address is registered
- POST /(api)/auth/reset-password validates the code, sets the new
  password, verifies the email, and signs the user in
- password_reset_codes table added to seed-db.mjs
- "Forgot password?" flow on the mobile sign-in screen

User deletion (new):
- DELETE /(api)/admin/users/[id], owner-only, blocks self-deletion
- Delete button with confirmation on the dashboard Users page

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

package-lock.json

@@ -39,6 +39,7 @@
         "expo-system-ui": "~3.0.7",
         "expo-web-browser": "~13.0.3",
         "nativewind": "^2.0.11",
+        "nodemailer": "^9.0.5",
         "pg": "^8.23.0",
         "prettier": "^3.3.3",
         "react": "18.2.0",
@@ -58,6 +59,7 @@
       "devDependencies": {
         "@babel/core": "^7.20.0",
         "@types/jest": "^29.5.12",
+        "@types/nodemailer": "^8.0.1",
         "@types/pg": "^8.23.1",
         "@types/react": "~18.2.45",
         "@types/react-test-renderer": "^18.0.7",
@@ -5950,6 +5952,15 @@
       "version": "8.3.0",
       "license": "MIT"
     },
+    "node_modules/@types/nodemailer": {
+      "version": "8.0.1",
+      "resolved": "https://registry.npmjs.org/@types/nodemailer/-/nodemailer-8.0.1.tgz",
+      "integrity": "sha512-PxpaInm8V1JQDd4j0ds5HfvWQk8JupS1C0Picb96QJsrrRDjBH+DlK7L4ZdNSqNULhiZRQHc40nLVShaGxXAMw==",
+      "dev": true,
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/parse-json": {
       "version": "4.0.2",
       "dev": true,
@@ -14188,6 +14199,14 @@
         "url": "https://github.com/sponsors/antelle"
       }
     },
+    "node_modules/nodemailer": {
+      "version": "9.0.5",
+      "resolved": "https://registry.npmjs.org/nodemailer/-/nodemailer-9.0.5.tgz",
+      "integrity": "sha512-wvjiKvjczmsN7U/8006JOdXubgBk2XFAbioDMbT+sM7cPs0QrhJTa6KBRX7P5REGGkDcLUz/EarWidb8G8C1jQ==",
+      "engines": {
+        "node": ">=6.0.0"
+      }
+    },
     "node_modules/normalize-path": {
       "version": "3.0.0",
       "license": "MIT",