* refactor(embed-core): update theme class names for consistency
Standardize theme class names to use 'cal-element-embed-dark' and 'cal-element-embed-light' to improve maintainability and clarity.
* refactor(embed-core): replace theme class strings with constants
* fix theme not changing
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Co-authored-by: Tushar Bhatt <95581504+TusharBhatt1@users.noreply.github.com>
Co-authored-by: Hariom <hariombalhara@gmail.com>