feat: automate promotions deployment routine

[LVT-ENG]

This pull request introduces a new, continuous background worker that automates the task of picking up new JSON files from promotions_inbox, validating their structure, and submitting the promotion to the production API (https://api.tryonyou.pro/v1/promotions). It addresses the need for a truly desatended process. Evaluated with internal test file and correctly manages successful vs. failed API calls natively in Python using time.sleep in an infinite loop.

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PR created automatically by Jules for task 12629463831592815706 started by @LVT-ENG

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