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>

test/test_config_live_in_ticker_migration.py

@@ -0,0 +1,108 @@
+"""live_in_ticker's new default reaches existing installs, once (src/config_manager.py).
+
+3.8.0 makes display.vegas_scroll.live_in_ticker true. Every existing config
+holds an explicit false copied from the template, which the template merge
+never touches (it only adds missing keys), so ConfigManager turns that false
+on once and marks the config. A false chosen after that -- the new checkbox,
+or by hand -- must stay false.
+"""
+
+import json
+import os
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+
+from src.config_manager import ConfigManager  # noqa: E402
+
+REPO = Path(__file__).resolve().parent.parent
+MARKER = ConfigManager.LIVE_IN_TICKER_MARKER
+
+
+@pytest.fixture
+def files(tmp_path):
+    template = {"display": {"brightness": 90,
+                            "vegas_scroll": {"enabled": False, "live_in_ticker": True}}}
+    paths = {name: tmp_path / f"{name}.json" for name in ("config", "secrets", "template")}
+    paths["template"].write_text(json.dumps(template))
+    paths["secrets"].write_text("{}")
+    return paths
+
+
+def _load(files, config):
+    files["config"].write_text(json.dumps(config))
+    manager = ConfigManager(config_path=str(files["config"]),
+                            secrets_path=str(files["secrets"]))
+    manager.template_path = str(files["template"])
+    manager.load_config()
+    return manager, json.loads(files["config"].read_text())
+
+
+def _vegas(saved):
+    return saved["display"]["vegas_scroll"]
+
+
+def test_the_old_default_is_turned_on_once_and_marked(files):
+    old = {"display": {"brightness": 90,
+                       "vegas_scroll": {"enabled": True, "live_in_ticker": False}}}
+    manager, saved = _load(files, old)
+    assert _vegas(saved)["live_in_ticker"] is True
+    assert _vegas(saved)[MARKER] is True
+    assert _vegas(manager.config)["live_in_ticker"] is True
+    # The config as it was is kept beside it.
+    backup = json.loads(Path(f"{files['config']}.backup").read_text())
+    assert _vegas(backup)["live_in_ticker"] is False
+
+
+def test_false_chosen_after_the_migration_stays_false(files):
+    chosen = {"display": {"brightness": 90,
+                          "vegas_scroll": {"enabled": True, "live_in_ticker": False,
+                                           MARKER: True}}}
+    _manager, saved = _load(files, chosen)
+    assert _vegas(saved)["live_in_ticker"] is False
+
+
+def test_a_marked_config_is_not_written_again(files):
+    marked = {"display": {"brightness": 90,
+                          "vegas_scroll": {"enabled": True, "live_in_ticker": True,
+                                           MARKER: True}}}
+    files["config"].write_text(json.dumps(marked))
+    before = files["config"].stat().st_mtime_ns
+    manager = ConfigManager(config_path=str(files["config"]),
+                            secrets_path=str(files["secrets"]))
+    manager.template_path = str(files["template"])
+    manager.load_config()
+    assert files["config"].stat().st_mtime_ns == before
+    assert not Path(f"{files['config']}.backup").exists()
+
+
+def test_a_config_without_vegas_settings_gets_the_new_default(files):
+    _manager, saved = _load(files, {"display": {"brightness": 90}})
+    assert _vegas(saved)["live_in_ticker"] is True
+    assert _vegas(saved)[MARKER] is True
+
+
+def test_true_already_is_only_marked(files):
+    on = {"display": {"brightness": 90,
+                      "vegas_scroll": {"enabled": True, "live_in_ticker": True}}}
+    _manager, saved = _load(files, on)
+    assert _vegas(saved)["live_in_ticker"] is True and _vegas(saved)[MARKER] is True
+
+
+def test_a_second_load_keeps_a_false_set_in_between(files):
+    old = {"display": {"brightness": 90,
+                       "vegas_scroll": {"enabled": True, "live_in_ticker": False}}}
+    _manager, saved = _load(files, old)
+    _vegas(saved)["live_in_ticker"] = False             # the checkbox, unticked
+    _manager, saved = _load(files, saved)
+    assert _vegas(saved)["live_in_ticker"] is False
+
+
+def test_the_shipped_template_has_the_new_default_and_never_the_marker():
+    template = json.loads((REPO / "config" / "config.template.json").read_text(encoding="utf-8"))
+    vegas = template["display"]["vegas_scroll"]
+    assert vegas["live_in_ticker"] is True
+    assert MARKER not in vegas