Refactor repo structure and add new icon sets

Restructured the repository from v1-v4 folders to a set-based organization
(set-1 through set-6) grouped by visual style rather than arbitrary version
numbers. Added new icon sets, dark theme variants, Lottie animations, and
a comprehensive icons.json mapping file.

sets/set-4/light/thunderstorms.svg

@@ -0,0 +1 @@
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