fix: address std-dev inline span refresh + style fixes (#19)

- A: create inline span when missing in refreshRoundHistory (was silently dropped)
- B: updateStdDevInline also called from refreshHistoryThenCalculate
- C: extract stdDevTooltipText + updateStdDevInline helpers; replace 3 call sites
- D: remove margin-left: 4px and bump font-size to 12px on .std-dev-inline
- E: guard against stdDev === 0 in EJS (truthy → != null)

views/partials/ratings-table.ejs

@@ -74,7 +74,7 @@ function renderSparkline(values, opts) {
                     <div class="pred-stack">
                         <span class="predicted-value pred-num mono" data-stddev="<%= player.stdDev || '' %>" data-pdga="<%= player.pdgaNumber %>"><%= player.predictedRating %></span>
                         <%- include('delta-pill', { value: player.deltaPredicted, extraClass: 'delta-predicted-pill' }) %>
-                        <% if (player.stdDev) { %><span class="std-dev-inline mono">±<%= player.stdDev %></span><% } %>
+                        <% if (player.stdDev != null) { %><span class="std-dev-inline mono">±<%= player.stdDev %></span><% } %>
                     </div>
                     <% } else { %>
                     <span class="rating-pending">—</span>