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.json

@@ -90,6 +90,7 @@
     "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",
@@ -109,6 +110,7 @@
   "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",