feat(vegas): keep live games in the ticker by default

display.vegas_scroll.live_in_ticker now defaults to true: through a live
game the marquee keeps running and the live scoreboard takes extra turns in
it -- its cards updating in place while they scroll -- instead of the ticker
giving way to the full-screen scoreboard.

The new default would reach nobody on its own: every existing config holds
an explicit false copied from the template (there was no control for it),
and the template merge only adds missing keys. ConfigManager therefore turns
a stored false on once, with a backup, and records live_in_ticker_migrated
so a false chosen afterwards stays. The marker is never in the template.

A "Keep live games in the ticker" checkbox under Vegas mode sets it. Tests
that pin the full-screen takeover now say live_in_ticker=false.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web_interface/blueprints/api_v3/config.py

@@ -802,7 +802,8 @@ def save_main_config():
                        'vegas_intra_plugin_gap', 'vegas_render_width_pct',
                        'vegas_min_content_separation', 'vegas_min_cut_gap',
                        'vegas_continuous_scroll', 'vegas_extend_threshold_screens',
-                       'vegas_smooth_scroll', 'vegas_overflow_mode', 'vegas_live_refresh']
+                       'vegas_smooth_scroll', 'vegas_overflow_mode', 'vegas_live_refresh',
+                       'vegas_live_in_ticker']
 
         if any(k in data for k in vegas_fields):
             if 'display' not in current_config:
@@ -823,6 +824,7 @@ def save_main_config():
             _set_checkbox(vegas_config, 'continuous_scroll', 'vegas_continuous_scroll')
             _set_checkbox(vegas_config, 'smooth_scroll', 'vegas_smooth_scroll')
             _set_checkbox(vegas_config, 'live_refresh', 'vegas_live_refresh')
+            _set_checkbox(vegas_config, 'live_in_ticker', 'vegas_live_in_ticker')
 
             # max_plugin_width_ratio is the one fractional setting, so it is
             # handled outside the integer loop below.