fix(mail): sync Object error, MIME subject decoding, sticky compact pagination

- Fix sync error: backend returns {synced, error?} not {success, synced_count}; frontend now checks error field
- Decode MIME encoded-words (=?UTF-8?Q?...?=) in backend during IMAP sync for subject/from/to/cc headers
- Add frontend decodeMimeHeader() utility for already-stored encoded subjects (MailList + MailDetail)
- Make pagination sticky at bottom of mail list (flex-col h-full, ul scrolls, pagination flex-shrink-0)
- Make pagination compact: smaller padding (px-1.5 py-0.5), text-xs, smaller icons, tighter spacing

frontend/src/api/mail.ts

@@ -381,8 +381,40 @@ export function testConnection(accountId: string): Promise<{ success: boolean; m
   return apiPost<{ success: boolean; message: string }>(`/mail/accounts/${accountId}/test-connection`);
 }
 
-export function triggerSync(accountId: string): Promise<{ success: boolean; synced_count: number }> {
-  return apiPost<{ success: boolean; synced_count: number }>(`/mail/accounts/${accountId}/sync`);
+export function triggerSync(accountId: string): Promise<{ synced: number; error?: string }> {
+  return apiPost<{ synced: number; error?: string }>(`/mail/accounts/${accountId}/sync`);
+}
+
+/**
+ * Decode MIME encoded-words (=?UTF-8?Q?...?=) to readable text.
+ * Used for mail subjects/from names that were stored before backend decoding was added.
+ */
+export function decodeMimeHeader(value: string | undefined | null): string {
+  if (!value) return '';
+  // Check if value contains MIME encoded-words
+  if (!value.includes('=?')) return value;
+  try {
+    // Decode all encoded-words in the string
+    return value.replace(/=\?([^?]+)\?([BQ])\?([^?]*)\?=/gi, (_match, _charset, encoding, encoded) => {
+      try {
+        if (encoding.toUpperCase() === 'B') {
+          // Base64 decode
+          const decoded = atob(encoded);
+          return decodeURIComponent(escape(decoded));
+        } else {
+          // Q encoding: replace _ with space, then decode =XX hex sequences
+          const qDecoded = encoded.replace(/_/g, ' ').replace(/=([0-9A-F]{2})/gi, (_m, hex) => {
+            return String.fromCharCode(parseInt(hex, 16));
+          });
+          return decodeURIComponent(escape(qDecoded));
+        }
+      } catch {
+        return _match;
+      }
+    });
+  } catch {
+    return value;
+  }
 }
 
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