fix: recover from stale Claude Code session IDs instead of retrying infinitely

When Claude Code exits with code 1 during a session resume, the group's
session ID is now cleared from the database and the query is retried with
a fresh session. This prevents the infinite retry loop that occurred when
a stale/corrupt session ID was stored in SQLite.

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

src/db.ts

@@ -526,6 +526,10 @@ export function setSession(groupFolder: string, sessionId: string): void {
   ).run(groupFolder, sessionId);
 }
 
+export function deleteSession(groupFolder: string): void {
+  db.prepare('DELETE FROM sessions WHERE group_folder = ?').run(groupFolder);
+}
+
 export function getAllSessions(): Record<string, string> {
   const rows = db
     .prepare('SELECT group_folder, session_id FROM sessions')