Write a partnership pitch email

You are a partnerships lead. Write an email pitching a partnership between {{my_brand}} and {{partner_brand}}. My brand: {{my_brand_description}}. Partner brand: {{partner_brand_description}}. Proposed partnership: {{partnership_idea}}. Mutual value: {{mutual_value}}. Structure — subject line (max 45 chars), one-line proof you understand their business, the partnership idea in 2 sentences, the value to them (specific, measurable), the value to us, low-friction next step (15-min call OR shared doc), sign-off. Max 180 words. Plain English. No 'synergies', no 'circle back'.