Fix group metadata sync setting epoch timestamp for new groups (#15)

updateChatName() was inserting new groups with last_message_time set to
Unix epoch (1970-01-01), causing newly discovered groups to appear at
the bottom of activity-ordered listings. Changed to use current time
for new groups while preserving existing timestamps for known groups.

https://claude.ai/code/session_018rcZvALfF3ND2jfcvBaFo2

Co-authored-by: Claude <noreply@anthropic.com>

src/db.ts

@@ -95,14 +95,15 @@ export function storeChatMetadata(chatJid: string, timestamp: string, name?: str
 }
 
 /**
- * Update chat name without changing timestamp.
+ * Update chat name without changing timestamp for existing chats.
+ * New chats get the current time as their initial timestamp.
  * Used during group metadata sync.
  */
 export function updateChatName(chatJid: string, name: string): void {
   db.prepare(`
     INSERT INTO chats (jid, name, last_message_time) VALUES (?, ?, ?)
     ON CONFLICT(jid) DO UPDATE SET name = excluded.name
-  `).run(chatJid, name, new Date(0).toISOString());
+  `).run(chatJid, name, new Date().toISOString());
 }
 
 export interface ChatInfo {