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/script.js

@@ -211,6 +211,7 @@ class MailManager {
         document.getElementById('backToAccounts').addEventListener('click', () => this.showAccountView());
         document.getElementById('mobileMailToggle').addEventListener('click', () => this.toggleMobileMailList());
         document.getElementById('mobileOverlay').addEventListener('click', () => this.closeMobileMailList());
+        document.getElementById('refreshEmailsBtn').addEventListener('click', () => this.refreshEmails());
     }
 
     // ====================================================================
@@ -495,7 +496,19 @@ class MailManager {
     // 邮件查看 — 数据
     // ====================================================================
 
-    async loadEmails() {
+    async refreshEmails() {
+        const btn = document.getElementById('refreshEmailsBtn');
+        btn.classList.add('spinning');
+        btn.disabled = true;
+        try {
+            await this.loadEmails(true);
+        } finally {
+            btn.classList.remove('spinning');
+            btn.disabled = false;
+        }
+    }
+
+    async loadEmails(refresh = false) {
         const container = document.getElementById('emailListContent');
         container.innerHTML = '<div class="loading-state"><div class="spinner-border spinner-border-sm"></div><p>加载邮件中...</p></div>';
 
@@ -505,6 +518,7 @@ class MailManager {
                 folder: this.currentFolder,
                 top: 20
             });
+            if (refresh) params.set('refresh', 'true');
             const resp = await fetch(`/api/messages?${params}`);
             const result = await resp.json();