feat(analytics): weekday by hour heatmap and posting volume chart

Frontend/src/components/analytics/PostingVolumeByHour.tsx

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+import React from 'react';
+
+export interface HourlyVolume {
+  hour: number;
+  volume: number;
+}
+
+export interface PostingVolumeByHourProps {
+  hourlyData?: HourlyVolume[];
+}
+
+export const PostingVolumeByHour: React.FC<PostingVolumeByHourProps> = ({
+  hourlyData = [],
+}) => {
+  const maxVolume = Math.max(...hourlyData.map(d => d.volume), 1);
+
+  return (
+    <div className="p-4 bg-white dark:bg-gray-900 rounded-lg border border-gray-200 dark:border-gray-800 shadow-sm">
+      <h3 className="text-lg font-semibold mb-2 text-gray-900 dark:text-gray-100">
+        Posting Volume by Hour of Day
+      </h3>
+      <div className="flex items-end h-40 gap-1 pt-4">
+        {Array.from({ length: 24 }).map((_, hour) => {
+          const item = hourlyData.find(d => d.hour === hour);
+          const vol = item ? item.volume : 0;
+          const heightPercent = (vol / maxVolume) * 100;
+          return (
+            <div key={hour} className="flex-1 flex flex-col items-center group">
+              <div className="w-full bg-gray-100 dark:bg-gray-800 h-full flex items-end rounded-t overflow-hidden">
+                <div
+                  className="w-full bg-indigo-500 group-hover:bg-indigo-400 transition-all rounded-t"
+                  style={{ height: `${heightPercent}%` }}
+                />
+              </div>
+              <span className="text-[10px] text-gray-400 mt-1 font-mono">{hour}h</span>
+            </div>
+          );
+        })}
+      </div>
+    </div>
+  );
+};
+
+export default PostingVolumeByHour;

Frontend/src/components/analytics/WeekdayHourHeatmap.tsx

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+import React from 'react';
+
+export interface WeekdayHourData {
+  day: string; // Mon, Tue, etc.
+  hour: number; // 0-23
+  count: number;
+}
+
+export interface WeekdayHourHeatmapProps {
+  data?: WeekdayHourData[];
+  onCellClick?: (day: string, hour: number) => void;
+}
+
+export const WeekdayHourHeatmap: React.FC<WeekdayHourHeatmapProps> = ({
+  data = [],
+  onCellClick,
+}) => {
+  const days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
+  const hours = Array.from({ length: 24 }, (_, i) => i);
+
+  const getIntensity = (day: string, hour: number) => {
+    const match = data.find(d => d.day === day && d.hour === hour);
+    return match ? match.count : 0;
+  };
+
+  return (
+    <div className="p-4 bg-white dark:bg-gray-900 rounded-lg shadow-sm border border-gray-200 dark:border-gray-800">
+      <h3 className="text-lg font-semibold mb-4 text-gray-900 dark:text-gray-100">
+        Weekday by Hour Posting Heatmap
+      </h3>
+      <div className="overflow-x-auto">
+        <div className="inline-block min-w-full">
+          <div className="grid grid-cols-25 gap-1 text-xs">
+            <div className="font-medium text-gray-500">Day</div>
+            {hours.map(h => (
+              <div key={h} className="text-center font-mono text-gray-400">
+                {h}
+              </div>
+            ))}
+            {days.map(day => (
+              <React.Fragment key={day}>
+                <div className="font-medium text-gray-600 dark:text-gray-300 py-1">{day}</div>
+                {hours.map(hour => {
+                  const val = getIntensity(day, hour);
+                  return (
+                    <button
+                      key={`${day}-${hour}`}
+                      onClick={() => onCellClick?.(day, hour)}
+                      className="w-full h-6 rounded transition-colors hover:ring-2 ring-indigo-500"
+                      style={{
+                        backgroundColor: val > 0 ? `rgba(99, 102, 241, ${Math.min(1, val / 50)})` : '#f3f4f6',
+                      }}
+                      title={`${day} ${hour}:00 - ${val} posts`}
+                    />
+                  );
+                })}
+              </React.Fragment>
+            ))}
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+};
+
+export default WeekdayHourHeatmap;