feat(vegas): let live content keep its place in the ticker

Live content used to preempt Vegas outright: while any plugin reported
live priority the display controller refused to run the ticker at all and
showed a full-screen scoreboard instead. Keeping the marquee meant not
seeing live scores; seeing live scores meant losing the marquee.

Two changes, both off by default.

vegas_scroll.live_in_ticker keeps the ticker running through a live game.
Three places assumed the takeover and all three now honour it: the
controller's gate, the coordinator's per-frame pause, and the rotation
switch that would otherwise move current_mode_index underneath a ticker
that never yields.

And the rotation is no longer a strict round robin. It was one slot per
plugin per cycle, so with a dozen plugins enabled a live score came round
once a lap and could be minutes old on screen. A plugin can now hold
several slots, placed by Smooth Weighted Round-Robin -- the same
scheduler the sports plugins already use to rotate their own games. The
property that matters is that repeats are spread through the cycle
rather than clumped: three in a row and then silence would be worse than
no boost at all.

Weight comes from the plugin first, via a new optional
get_vegas_priority_weight(), then from the core: live content earns
live_weight, everything else 1. So existing plugins gain the behaviour
without changes, and the hook exists for the one thing the core cannot
work out -- the core can see that a game is live but not whose, so only
the plugin can say a favorite is playing.

Documented in ADVANCED_FEATURES (worked example, why weights are per
plugin not per game, and that frequency is not freshness),
CONFIG_REFERENCE, PLUGIN_API_REFERENCE, and the config template.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Udr6MfaFLUPhX5Fgo67Jf5

docs/PLUGIN_API_REFERENCE.md

@@ -170,6 +170,45 @@ Default returns `False`.
 List of display modes to show during a live takeover. Default returns the
 plugin's `display_modes` from its manifest.
 
+#### `get_vegas_priority_weight() -> Optional[int]`
+
+How many slots per Vegas cycle this plugin should get. Default returns
+`None`, which defers to the core.
+
+The Vegas ticker is otherwise a strict round robin — every plugin appears
+exactly once per cycle — so with a dozen plugins enabled a live score can be
+minutes stale by the time it comes round. A weight of *N* gives the plugin
+*N* slots per cycle, spread evenly through it rather than clumped.
+
+**You usually do not need this.** When the hook returns `None`, the core
+already gives a plugin `vegas_scroll.live_weight` whenever
+`has_live_priority()` and `has_live_content()` are both true. Live sports get
+extra turns with no code at all.
+
+Implement it only when the plugin knows something the core cannot. The
+motivating case is favorite teams — the core can see *that* a game is live,
+but not *whose*:
+
+```python
+def get_vegas_priority_weight(self):
+    if not (self.has_live_priority() and self.has_live_content()):
+        return None                       # let the core decide
+    vegas = self.global_config.get('display', {}).get('vegas_scroll', {})
+    if self._favorite_is_live():
+        return vegas.get('favorite_live_weight', 5)
+    return vegas.get('live_weight', 3)
+```
+
+The weight is per *plugin*, not per game: a scoreboard showing four live games
+still occupies one slot at a time and rotates its own games within it. Values
+are clamped to 1–10 by the caller, and an exception here is caught and
+treated as weight 1 rather than breaking the rotation.
+
+Only consulted when the user has set `vegas_scroll.live_in_ticker`. With the
+default (`false`) live content preempts Vegas entirely and there is no ticker
+to be weighted within. See
+[ADVANCED_FEATURES.md](ADVANCED_FEATURES.md#live-content-in-the-ticker).
+
 ### Vegas scroll hooks
 
 Vegas mode shows multiple plugins as a single continuous scroll instead of