fix: conversion audit — fix all broken CTAs, wrong data claims, hero rewrite

CRITICAL:
- Fix broken mailto: CTAs on /offer and /proposal (empty href!)
- Fix 97.4% channel dependency claim → actual 85% (verified from DB)
- Fix 37.3% repeat rate → 57.6% cohort return rate (verified)
- Fix revenue model payback math (was 2.6mo, actual 3.5mo at 100/mo)
- Fix cost-of-waiting claim with verifiable math

CONVERSION:
- Hero rewrite: 'Lost 84% of new customers' → client problem, not tech brag
- Nav: remove duplicate Proposal link, single 'The Proposal' → /offer
- Footer CTA: primary action is now 'See the Full Proposal'
- All CTAs now include properly formatted mailto with subject+body
- Replace unverified competitor claim with specific named competitors

DATA INTEGRITY:
- 15/23 claims verified SOURCE-LINKED from PostgreSQL (728K orders)
- 4 claims corrected (97.4%→85%, 37.3%→57.6%, payback, cost-of-waiting)
- Revenue calculator uses cohort-verified return rate
- Board summary updated with correct figures

static/proposal/index.html

@@ -1010,7 +1010,7 @@ section.visible {
     <div class="cta-box">
       <div class="cta-title">Ready to Build?</div>
       <p class="cta-desc">If approved, access is provided and build starts immediately. Fully operational in 3–4 weeks.</p>
-      <a class="cta-button" href="mailto:">
+      <a class="cta-button" href="mailto:omair@quikcue.com?subject=JustVitamin%20AI%20Infrastructure%20%E2%80%94%20Approved%20to%20Start&body=Hi%20Omair%2C%0A%0AApproved%20to%20proceed%20with%20the%20AI%20infrastructure%20build.%0ALet%E2%80%99s%20schedule%20the%20kickoff%20call.%0A%0AThanks">
         Let's Go →
       </a>
       <div class="cta-footer">