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>

schema.sql

@@ -59,6 +59,14 @@ CREATE TABLE IF NOT EXISTS verification_codes (
     used       INTEGER NOT NULL DEFAULT 0
 );
 
+CREATE TABLE IF NOT EXISTS sms_consents (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    phone      TEXT    NOT NULL,
+    ip_address TEXT    NOT NULL DEFAULT '',
+    user_agent TEXT    NOT NULL DEFAULT '',
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
 CREATE INDEX IF NOT EXISTS idx_slots_event ON slots(event_id);
 CREATE INDEX IF NOT EXISTS idx_claims_slot ON claims(slot_id);
 CREATE INDEX IF NOT EXISTS idx_rsvps_event ON rsvps(event_id);