refactor: move std-dev info to accordion, remove tooltip (#19)

- Add "Round spread" row (±stdDev, range lo–hi) to desktop accordion
  (player-history.ejs) and mobile card expanded section (ratings-cards.ejs)
- Remove .std-dev-tooltip div and .std-dev-inline span from table partial
- Remove stdDevTooltipText, updateStdDevInline, initRatingsTooltips helpers
  and all call sites from players.js
- Remove .std-dev-tooltip and .std-dev-inline CSS rules; drop cursor:help
  from .rating-value

views/partials/ratings-cards.ejs

@@ -114,6 +114,12 @@ function renderSparkline(values, opts) {
                     <dt>Gap to predicted</dt>
                     <dd><span class="delta-pill <%= predCls %> delta-predicted-pill"><span class="delta-glyph"><%= predGlyph %></span><span class="delta-num"><%= predNum %></span></span></dd>
                 </div>
+                <% if (player.stdDev != null && player.rating) { %>
+                <div>
+                    <dt>Round spread</dt>
+                    <dd>±<%= player.stdDev %> (range <%= player.rating - player.stdDev %>–<%= player.rating + player.stdDev %>)</dd>
+                </div>
+                <% } %>
             </dl>
         </div>
     </div>