Adds get_all_programs(), get_program(), get_program_by_slug() for admin
CRUD. Adds build_affiliate_url() that assembles URLs from program template
+ product identifier, with fallback to baked affiliate_url for legacy
products. Updates get_product() to JOIN affiliate_programs so _program
dict is available at redirect time. _parse_product() extracts program
fields into nested _program key.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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