Add Redis caching, email refresh button, optimize page loading

- Add Redis service (docker-compose) for caching accounts, messages, payment status
- Cache accounts list (5min), messages (3min), payment status (10min)
- Auto-invalidate cache on import/delete/payment-check/note-update
- Add refresh button to email list panel (force re-fetch from IMAP)
- Messages API supports refresh=true param to bypass cache
- New cache.py module with RedisCache class

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

static/style.css

@@ -731,6 +731,19 @@ body {
     flex-shrink: 0;
 }
 
+.email-refresh-btn {
+    margin-left: auto;
+    width: 30px;
+    height: 30px;
+    font-size: 14px;
+    border: none;
+    flex-shrink: 0;
+}
+
+.email-refresh-btn.spinning i {
+    animation: spin 0.6s linear infinite;
+}
+
 .email-count-badge {
     display: inline-flex;
     align-items: center;