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/en.json

@@ -1192,6 +1192,10 @@
     "color_strip.composite.error.min_layers": "At least 1 layer is required",
     "color_strip.composite.error.no_source": "Each layer must have a source selected",
     "color_strip.composite.layers_count": "layers",
+    "color_strip.composite.range": "LED Range",
+    "color_strip.composite.range_start": "Start",
+    "color_strip.composite.range_end": "End",
+    "color_strip.composite.reverse": "Reverse",
     "color_strip.mapped.zones": "Zones:",
     "color_strip.mapped.zones.hint": "Each zone maps a color strip source to a specific LED range. Zones are placed side-by-side — gaps between zones stay black.",
     "color_strip.mapped.add_zone": "+ Add Zone",