overview: add missing axis labels to supply/demand, STU, and top-producers charts

- Supply & Demand chart: Y-axis → '1,000 60-kg bags'
- Stock-to-Use chart: Y-axis → 'Stock-to-Use (%)'
- Top Producers bar: X-axis → '1,000 60-kg bags'
- YoY table: Production column header → 'Production (1k bags)'

COT, price, ICE stocks, aging, and by-port charts already had labels.

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

web/src/beanflows/dashboard/templates/index.html

@@ -81,7 +81,7 @@
           <thead>
             <tr>
               <th>Country</th>
-              <th class="text-right">Production</th>
+              <th class="text-right">Production (1k bags)</th>
               <th class="text-right">YoY %</th>
             </tr>
           </thead>
@@ -349,7 +349,7 @@ if (tsData.length > 0) {
     options: {
       responsive: true,
       plugins: {legend: {position: 'bottom'}},
-      scales: {y: {beginAtZero: false}}
+      scales: {y: {title: {display: true, text: '1,000 60-kg bags'}, beginAtZero: false}}
     }
   });
 }
@@ -373,7 +373,7 @@ if (stuData.length > 0) {
     options: {
       responsive: true,
       plugins: {legend: {display: false}},
-      scales: {y: {beginAtZero: false}}
+      scales: {y: {title: {display: true, text: 'Stock-to-Use (%)'}, beginAtZero: false}}
     }
   });
 }
@@ -597,7 +597,7 @@ if (topData.length > 0) {
       indexAxis: 'y',
       responsive: true,
       plugins: {legend: {display: false}},
-      scales: {x: {beginAtZero: true}}
+      scales: {x: {title: {display: true, text: '1,000 60-kg bags'}, beginAtZero: true}}
     }
   });
 }