fix(vegas): stop capping plugin width by default

Vegas plugins read as "cut off early" or "starting in the middle". That
was the per-plugin width budget, not the scroll engine:
overflow_mode=rotate is designed to resume mid-content on each
appearance, so the symptom was the feature working as specified.

Measured over a 17-plugin fleet on a 512px panel, the cap was a bad
trade. Only four plugins were ever wide enough to hit the 3.0 default --
leaderboard 11,518px, news 10,021px, odds-ticker 4,643px, hockey
1,508px. Weather is 650px and flights 512px; the cap never touched them
or the other eleven. So it bought nothing on thirteen plugins while
costing two visible faults on four: content entering mid-item (a news
ticker started at column 6027 of its own strip), and a final rotation
window of whatever happened to be left -- 348px of an 1,840px stocks
ticker, seven seconds of panel time.

Default max_plugin_width_ratio to 0 (uncapped), so every plugin
contributes all of its content and is always entered at its beginning.
The cap remains available, and vegas_max_width_screens still caps an
individual plugin -- which is where the knob belongs, since a genuinely
long ticker is a property of that plugin rather than of the fleet.

Verified on a live 512px device: 327 budget crops in the preceding six
hours, none after.

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

test/test_vegas_density.py

@@ -781,6 +781,12 @@ class TestNewConfigKeys:
         assert cfg.render_width_pct == 100
         assert cfg.min_content_separation == 24
 
+    def test_width_cap_is_off_by_default(self):
+        # Capping made wide plugins resume mid-content on every appearance and
+        # emit runt final windows; it is now opt-in per plugin instead.
+        assert VegasModeConfig().max_plugin_width_ratio == 0.0
+        assert VegasModeConfig.from_config({}).max_plugin_width_ratio == 0.0
+
     @pytest.mark.parametrize('overrides,bad_key', [
         ({'render_width_pct': 5}, 'render_width_pct'),
         ({'render_width_pct': 101}, 'render_width_pct'),