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>

index.html

@@ -489,7 +489,24 @@
           </div>
         </div>
         <p class="calc-error hidden" id="calcError">Please fill in homesites and annual dues income to continue.</p>
-        <button class="btn btn-primary btn-lg calc-submit-btn" id="calcSubmit">Calculate My Potential →</button>
+        <!-- Email + opt-in -->
+        <div class="calc-email-row">
+          <div class="calc-field calc-field--full">
+            <label for="calcEmail">Your Email Address <span class="calc-optional">(optional)</span></label>
+            <input type="email" id="calcEmail" placeholder="you@example.com" />
+          </div>
+          <label class="calc-optin-label">
+            <input type="checkbox" id="calcOptIn" checked />
+            <span>I'd like LedgerIQ to follow up with a refined, community-specific estimate</span>
+          </label>
+          <p class="calc-privacy">🔒 Your email and submitted data are used solely to provide your ROI estimate and will never be shared with any third party or outside organization.</p>
+        </div>
+
+        <p class="calc-error hidden" id="calcError">Please fill in homesites and annual dues income to continue.</p>
+        <button class="btn btn-primary btn-lg calc-submit-btn" id="calcSubmit">
+          <span class="calc-btn-text">Calculate My Potential →</span>
+          <span class="calc-btn-loading hidden"><span class="calc-spinner"></span> Calculating…</span>
+        </button>
         <p class="calc-fine">Conservative estimates for illustrative purposes only. Not financial advice.</p>
       </div>
 
@@ -520,6 +537,11 @@
           <p id="calcAiText"></p>
         </div>
 
+        <div class="calc-refine-blurb">
+          <span class="calc-refine-icon">⚙</span>
+          <p>This is a high-level estimate based on your inputs. Inside HOA LedgerIQ, your investment strategy is continuously refined against your live cash flows, upcoming expenses, and reserve study timelines — automatically maximizing yield while keeping your community fully liquid.</p>
+        </div>
+
         <div class="calc-cta">
           <p>Ready to put these gains to work for your community?</p>
           <a href="#preview-signup" class="btn btn-primary btn-lg calc-cta-btn" id="calcCTABtn">Get Early Access — Reserve My Spot →</a>