Daily login bonus (streak) + solo-ad budget default

- Daily login bonus: once/day, base 5 credits + gentle streak (+1/day, cap +5)
  for consecutive days; granted after sign-in, toast + cha-ching. New
  login_day/login_streak on earned_credits; /api/my/login-bonus.
- Solo ad: selecting Solo now defaults Budget to 50 credits (5cr x 10 min
  deliveries) so entering 10 isn't rejected after submit.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

db.js

@@ -72,6 +72,8 @@ async function bootstrap() {
   ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4`);
   const alterSafe0 = async sql => { try { await q(sql); } catch (e) { if (!['ER_DUP_FIELDNAME', 'ER_DUP_KEYNAME'].includes(e.code)) throw e; } };
   await alterSafe0('ALTER TABLE earned_credits ADD COLUMN milestones VARCHAR(255) NULL'); // comma-joined granted milestone keys
+  await alterSafe0('ALTER TABLE earned_credits ADD COLUMN login_day CHAR(10) NULL');   // last daily-login-bonus day
+  await alterSafe0('ALTER TABLE earned_credits ADD COLUMN login_streak INT NOT NULL DEFAULT 0'); // consecutive-day streak
   // additive columns (MySQL 8 has no IF NOT EXISTS for columns)
   const alterSafe = async sql => {
     try { await q(sql); }