Upgrade: Auto Match End + Winner Hold + Next Match Toss Overlay

Added:
1. Second innings target reached => match auto completes immediately.
2. Completed match blocks further score updates.
3. Winner Congratulations center overlay stays on screen until next match starts.
4. Removed old top-right Next Match overlay behavior.
5. Added Dashboard > Next Match Overlay card:
   - Select next match
   - Select toss winner
   - Select toss choice: Bat / Bowl / Field
   - Show / Hide center overlay
6. Next Match overlay displays large center card with team logos, team names, toss winner and choice.
7. Starting/resuming a match automatically hides the next match overlay.

Database additions are auto-migrated when api/get_score.php or api/overlay_control.php runs:
- match_state.next_match_overlay_visible
- match_state.next_match_overlay_match_id
- match_state.toss_winner_team_id
- match_state.toss_choice
- same fields in match_snapshots