Add SMS consent logging for Twilio compliance

Log phone, IP, and user agent to sms_consents table before sending
verification SMS. Add disclosure text to login form.

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

db/models.go

@@ -54,6 +54,14 @@ type Slot struct {
 	SortOrder int64
 }
 
+type SmsConsent struct {
+	ID        int64
+	Phone     string
+	IpAddress string
+	UserAgent string
+	CreatedAt time.Time
+}
+
 type User struct {
 	ID        int64
 	Phone     sql.NullString