Add bottle size, bourbon list modal, and stat improvements

- Add bottle_size field to User model and UserResponse/UserUpdate schemas
- Settings modal includes bottle size input (shots capacity)
- Community bottles and My Bottle page show fill bar based on bottle size
- Community bottle cards are clickable — opens searchable bourbon list modal
- Add total_shots_added stat to replace duplicate net volume on dashboard
- Reorder dashboard stats: Bourbons Added, Total Poured In, Shots Remaining, Est. Proof
- Theme-matched custom scrollbar (amber on dark)

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

frontend/js/auth.js

@@ -114,10 +114,14 @@ const Auth = (() => {
           <div id="settings-msg"></div>
 
           <h3 class="settings-section-title">Profile</h3>
-          <div class="form-group" style="margin-bottom:1.25rem">
+          <div class="form-group">
             <label for="settings-display-name">Display Name</label>
             <input type="text" id="settings-display-name" value="${escHtml(user?.display_name || '')}" maxlength="100" />
           </div>
+          <div class="form-group" style="margin-bottom:1.25rem">
+            <label for="settings-bottle-size">Bottle Size (shots)</label>
+            <input type="number" id="settings-bottle-size" value="${user?.bottle_size ?? ''}" min="1" step="0.5" placeholder="e.g. 25" />
+          </div>
 
           <hr class="settings-divider">
 
@@ -179,10 +183,12 @@ const Auth = (() => {
   }
 
   async function saveProfile() {
-    const displayName = document.getElementById('settings-display-name').value.trim();
-    const timezone    = document.getElementById('settings-tz').value;
+    const displayName  = document.getElementById('settings-display-name').value.trim();
+    const timezone     = document.getElementById('settings-tz').value;
+    const bottleSizeRaw = document.getElementById('settings-bottle-size').value;
+    const bottleSize   = bottleSizeRaw !== '' ? parseFloat(bottleSizeRaw) : null;
     try {
-      const user = await API.users.update({ display_name: displayName || null, timezone });
+      const user = await API.users.update({ display_name: displayName || null, timezone, bottle_size: bottleSize });
       saveUser(user);
       const usernameEl = document.querySelector('.nav-username');
       if (usernameEl) usernameEl.textContent = user.display_name || user.email || 'Account';