fix: resolve 4 logic bugs found in code review

- utc_to_eastern: use zoneinfo instead of hardcoded EDT offset (-4)
  so start times are correct in both EST and EDT
- standings: fetch before truncate so a failed API call doesn't wipe
  existing standings data
- routes: call parse_games() once per request instead of three times
- scheduler: wrap run_pending() in try/except so an unhandled exception
  doesn't kill the background thread

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/standings.py

@@ -67,8 +67,8 @@ def fetch_standings():
 def refresh_standings():
     conn = sqlite3.connect(DB_PATH)
     create_standings_table(conn)
-    truncate_standings_table(conn)
     standings = fetch_standings()
     if standings:
+        truncate_standings_table(conn)
         insert_standings(conn, standings)
     conn.close()