Add calculator UX enhancements and submission tracking

- Button loading spinner + disable on submit to prevent duplicate AI calls
- Email field and opt-in consent checkbox on calculator form (checked by default)
- Privacy assurance blurb below opt-in
- Refinement blurb on results screen explaining live cash-flow optimization
- calc_submissions SQLite table stores form inputs, computed results, AI text, email, opt-in
- GET /api/calc-submissions endpoint (x-admin-key protected) to retrieve submissions

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

app.js

@@ -52,6 +52,16 @@
     close();
   });
 
+  const calcBtnText    = submitBtn?.querySelector('.calc-btn-text');
+  const calcBtnLoading = submitBtn?.querySelector('.calc-btn-loading');
+
+  function setCalcLoading(on) {
+    if (!submitBtn) return;
+    submitBtn.disabled = on;
+    calcBtnText?.classList.toggle('hidden', on);
+    calcBtnLoading?.classList.toggle('hidden', !on);
+  }
+
   submitBtn?.addEventListener('click', async () => {
     const homesites    = parseFloat(document.getElementById('calcHomesites').value)    || 0;
     const propertyType = document.getElementById('calcPropertyType').value;
@@ -59,12 +69,15 @@
     const paymentFreq  = document.getElementById('calcPaymentFreq').value;
     const reserveFunds = parseFloat(document.getElementById('calcReserveFunds').value) || 0;
     const interest2025 = parseFloat(document.getElementById('calcInterest2025').value) || 0;
+    const calcEmail    = document.getElementById('calcEmail')?.value.trim() || '';
+    const calcOptIn    = document.getElementById('calcOptIn')?.checked ?? true;
 
     if (!homesites || !annualIncome) {
       calcErr.classList.remove('hidden');
       return;
     }
     calcErr.classList.add('hidden');
+    setCalcLoading(true);
 
     // ── Conservative investment assumptions ──
     // Operating cash: depending on payment frequency, portion investable in high-yield savings
@@ -121,7 +134,11 @@
       const aiRes = await fetch('/api/calculate', {
         method:  'POST',
         headers: { 'Content-Type': 'application/json' },
-        body:    JSON.stringify({ homesites, propertyType, annualIncome, paymentFreq, reserveFunds, interest2025 }),
+        body:    JSON.stringify({
+          homesites, propertyType, annualIncome, paymentFreq, reserveFunds, interest2025,
+          email: calcEmail, optIn: calcOptIn,
+          totalPotential, opInterest, resInterest,
+        }),
       });
       if (aiRes.ok) {
         const { recommendation } = await aiRes.json();
@@ -136,6 +153,7 @@
     // ── Animate the main number ──
     animateValue(document.getElementById('resultAmount'), 0, totalPotential);
 
+    setCalcLoading(false);
     calcForm.classList.add('hidden');
     calcRes.classList.remove('hidden');
   });