feat: add per-layer LED range and collapsible layers to composite source

Composite layers now support optional start/end LED range (toggleable)
and reverse flag, making composite a superset of mapped source. Layers
are collapsible with animated expand/collapse and consistent 0.85rem
font sizing. Delete button restyled as ghost icon button.

Also includes minor dashboard CSS overflow fixes.

server/src/wled_controller/static/locales/zh.json

@@ -1157,6 +1157,10 @@
     "color_strip.composite.error.min_layers": "至少需要 1 个图层",
     "color_strip.composite.error.no_source": "每个图层必须选择一个源",
     "color_strip.composite.layers_count": "个图层",
+    "color_strip.composite.range": "LED范围",
+    "color_strip.composite.range_start": "起始",
+    "color_strip.composite.range_end": "结束",
+    "color_strip.composite.reverse": "反转",
     "color_strip.mapped.zones": "区域：",
     "color_strip.mapped.zones.hint": "每个区域将色带源映射到特定 LED 范围。区域并排放置 — 区域之间的间隙保持黑色。",
     "color_strip.mapped.add_zone": "+ 添加区域",