fix: aggregation (#30)

* feat: add aggregation support for custom event tracking

- Add aggregation parameter (day/week/month) to custom events API endpoint
- Implement aggregation logic in service layer for custom events
- Add helper methods for weekly and monthly aggregation of custom events
- Create comprehensive test suite (9 tests) for custom event aggregation
- Ensure custom events are grouped by dashboard aggregation setting
- All 18 aggregation tests pass (9 dashboard + 9 custom events)

This allows users to view custom event data aggregated by day, week, or
month, matching the behavior of regular analytics events.

* fix: pass aggregation parameter from frontend to custom events API

The custom events timeseries API was not receiving the aggregation
parameter from the frontend, causing it to always default to daily
aggregation regardless of the user's selection.

Changes:
- Add aggregation parameter to custom events API call
- Update chart time unit based on aggregation (day/week/month)
- Dynamically adjust chart display format for different aggregations

Now when users change the aggregation period, custom events will
properly group by day, week, or month matching the regular events.

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: psincraian

app/src/js/dashboard.js

@@ -668,6 +668,12 @@ async function loadCustomEventsTimeseries() {
     try {
         const params = buildQueryParams();
         const eventTypesParam = Array.from(selectedEventTypes).join(',');
+
+        // Add aggregation parameter
+        if (currentAggregation) {
+            params.append('aggregation', currentAggregation);
+        }
+
         const response = await fetch(`/api/dashboard/custom-events/timeseries?event_types=${encodeURIComponent(eventTypesParam)}&${params}`);
 
         if (!response.ok) {
@@ -718,6 +724,18 @@ function renderCustomEventsChart(data) {
         };
     });
 
+    // Determine time unit based on aggregation
+    let timeUnit = 'day';
+    let displayFormat = 'MMM d';
+
+    if (currentAggregation === 'week') {
+        timeUnit = 'week';
+        displayFormat = 'MMM d';
+    } else if (currentAggregation === 'month') {
+        timeUnit = 'month';
+        displayFormat = 'MMM yyyy';
+    }
+
     // Create chart
     customEventsChart = new Chart(ctx, {
         type: 'line',
@@ -754,9 +772,11 @@ function renderCustomEventsChart(data) {
                 x: {
                     type: 'time',
                     time: {
-                        unit: 'day',
+                        unit: timeUnit,
                         displayFormats: {
-                            day: 'MMM d'
+                            day: 'MMM d',
+                            week: 'MMM d',
+                            month: 'MMM yyyy'
                         }
                     },
                     grid: {