Support both email and phone login

Auto-detect whether the user entered an email or phone number.
Email sends via Resend, phone sends via Twilio SMS. Users table
has nullable phone and email columns; verification_codes uses a
generic identifier field.

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

migrate.go

@@ -10,8 +10,11 @@ func runMigrations(database *sql.DB) {
 	migrations := []string{
 		`ALTER TABLE events ADD COLUMN description TEXT DEFAULT ''`,
 		`ALTER TABLE events ADD COLUMN user_id INTEGER REFERENCES users(id)`,
-		`ALTER TABLE users RENAME COLUMN email TO phone`,
-		`ALTER TABLE verification_codes RENAME COLUMN email TO phone`,
+		// Users may have email, phone, or both. Add whichever column is missing.
+		`ALTER TABLE users ADD COLUMN phone TEXT UNIQUE`,
+		`ALTER TABLE users ADD COLUMN email TEXT UNIQUE`,
+		// Verification codes use a generic identifier column.
+		`ALTER TABLE verification_codes ADD COLUMN identifier TEXT NOT NULL DEFAULT ''`,
 	}
 	for _, m := range migrations {
 		_, err := database.Exec(m)