Add interest income benefit calculator widget to hero

- New "✦ Calculate Your Interest Income Potential" button between hero CTAs
  with gradient border styling distinct from primary/ghost buttons
- Modal overlay collects: homesites, property type, annual dues + frequency,
  reserve fund balance, and 2025 actual interest income
- Conservative calculation model: 4.0% HYSA for operating cash, 4.25% CD
  ladder for 65% of investable reserves; operating multiplier varies by
  payment frequency (monthly 10%, quarterly 20%, annual 35%)
- Results screen shows animated dollar counter, operating vs reserve
  breakdown, AI-style narrative recommendation, and direct CTA to signup
- Modal closes on backdrop click or Escape key; CTA closes modal and
  scrolls to early access signup form

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.js

@@ -20,6 +20,124 @@
   if (signupEl) signupEl.textContent = text;
 })();
 
+// ── Benefit Calculator ───────────────────────────────────
+(function initCalculator() {
+  const overlay   = document.getElementById('calcOverlay');
+  const openBtn   = document.getElementById('openCalc');
+  const closeBtn  = document.getElementById('calcClose');
+  const submitBtn = document.getElementById('calcSubmit');
+  const recalcBtn = document.getElementById('calcRecalc');
+  const calcForm  = document.getElementById('calcForm');
+  const calcRes   = document.getElementById('calcResults');
+  const calcErr   = document.getElementById('calcError');
+  const ctaBtn    = document.getElementById('calcCTABtn');
+
+  if (!overlay) return;
+
+  function open()  { overlay.classList.add('open'); document.body.style.overflow = 'hidden'; }
+  function close() { overlay.classList.remove('open'); document.body.style.overflow = ''; }
+
+  openBtn?.addEventListener('click', open);
+  closeBtn?.addEventListener('click', close);
+  overlay.addEventListener('click', e => { if (e.target === overlay) close(); });
+  document.addEventListener('keydown', e => { if (e.key === 'Escape') close(); });
+
+  recalcBtn?.addEventListener('click', () => {
+    calcRes.classList.add('hidden');
+    calcForm.classList.remove('hidden');
+  });
+
+  // Close modal and scroll to signup when CTA clicked
+  ctaBtn?.addEventListener('click', () => {
+    close();
+  });
+
+  submitBtn?.addEventListener('click', () => {
+    const homesites    = parseFloat(document.getElementById('calcHomesites').value)    || 0;
+    const propertyType = document.getElementById('calcPropertyType').value;
+    const annualIncome = parseFloat(document.getElementById('calcAnnualIncome').value) || 0;
+    const paymentFreq  = document.getElementById('calcPaymentFreq').value;
+    const reserveFunds = parseFloat(document.getElementById('calcReserveFunds').value) || 0;
+    const interest2025 = parseFloat(document.getElementById('calcInterest2025').value) || 0;
+
+    if (!homesites || !annualIncome) {
+      calcErr.classList.remove('hidden');
+      return;
+    }
+    calcErr.classList.add('hidden');
+
+    // ── Conservative investment assumptions ──
+    // Operating cash: depending on payment frequency, portion investable in high-yield savings
+    const opMultiplier  = { monthly: 0.10, quarterly: 0.20, annually: 0.35 }[paymentFreq] || 0.10;
+    const opRate        = 0.040;   // 4.0% money market / HYSA
+    const resRatio      = 0.65;    // 65% of reserves investable (keep 35% liquid)
+    const resRate       = 0.0425;  // 4.25% CD ladder / short-term treasuries
+
+    const investableOp  = annualIncome * opMultiplier;
+    const investableRes = reserveFunds * resRatio;
+    const opInterest    = Math.round(investableOp  * opRate);
+    const resInterest   = Math.round(investableRes * resRate);
+    const totalPotential = opInterest + resInterest;
+    const increase       = totalPotential - interest2025;
+    const pctIncrease    = interest2025 > 0
+      ? Math.round((increase / interest2025) * 100)
+      : (totalPotential > 0 ? 100 : 0);
+
+    // ── Populate results ──
+    const fmt = n => '$' + Math.round(n).toLocaleString();
+
+    document.getElementById('resultAmount').textContent   = fmt(totalPotential);
+    document.getElementById('resultCurrent').textContent  = fmt(interest2025);
+    document.getElementById('resultOperating').textContent = fmt(opInterest);
+    document.getElementById('resultReserve').textContent   = fmt(resInterest);
+
+    const badge = document.getElementById('resultBadge');
+    if (increase > 0) {
+      badge.textContent = `+${fmt(increase)} · +${pctIncrease}%`;
+      badge.style.display = 'inline-block';
+    } else {
+      badge.style.display = 'none';
+    }
+
+    // ── AI-style suggestion text ──
+    const typeLabels = { sfh:'single-family home', townhomes:'townhome', condos:'condo', mixed:'mixed-use', '':'' };
+    const typeLabel  = typeLabels[propertyType] || '';
+    const freqLabel  = { monthly:'monthly', quarterly:'quarterly', annually:'annual' }[paymentFreq];
+    const communityDesc = [homesites && `${homesites}-unit`, typeLabel, 'community'].filter(Boolean).join(' ');
+
+    let ai = `Based on your ${communityDesc} collecting ${fmt(annualIncome)} in ${freqLabel} dues`;
+    if (reserveFunds > 0) ai += ` and ${fmt(reserveFunds)} in reserve funds`;
+    ai += `, a conservative investment strategy could generate approximately ${fmt(totalPotential)} in annual interest income. `;
+    if (resInterest > 0) ai += `Deploying ${fmt(investableRes)} of your reserve funds into a short-term CD ladder at ~4.25% yields ${fmt(resInterest)} annually. `;
+    if (opInterest > 0)  ai += `Keeping a ${fmt(investableOp)} operating cash buffer in a high-yield money market at ~4.0% adds another ${fmt(opInterest)}. `;
+    if (interest2025 > 0 && increase > 0) {
+      ai += `That's a ${fmt(increase)} improvement (+${pctIncrease}%) over your 2025 interest income of ${fmt(interest2025)} — with no additional risk.`;
+    } else if (interest2025 === 0) {
+      ai += `This would represent entirely new interest income for your community at no additional risk.`;
+    }
+
+    document.getElementById('calcAiText').textContent = ai;
+
+    // ── Animate the main number ──
+    animateValue(document.getElementById('resultAmount'), 0, totalPotential);
+
+    calcForm.classList.add('hidden');
+    calcRes.classList.remove('hidden');
+  });
+
+  function animateValue(el, from, to) {
+    const duration = 900;
+    const start = performance.now();
+    function step(now) {
+      const progress = Math.min((now - start) / duration, 1);
+      const ease = 1 - Math.pow(1 - progress, 3);
+      el.textContent = '$' + Math.round(from + (to - from) * ease).toLocaleString();
+      if (progress < 1) requestAnimationFrame(step);
+    }
+    requestAnimationFrame(step);
+  }
+})();
+
 // ── Screenshot Carousel ──────────────────────────────────
 (function initCarousel() {
   const carousel = document.getElementById('screenshotCarousel');