Notification Aggregation / Digest Mode

[shepilov]

Summary

Instead of silently dropping notifications during the MinInterval period, collect them and send a single aggregated email with a summary of all events.

Context

Current behavior with MinInterval:
User uploads 50 files in 5 minutes, MinInterval = 30 minutes

• 00:00 - File 1 uploaded → Email sent ✓
• 00:01 - File 2 uploaded → SKIPPED
• 00:02 - File 3 uploaded → SKIPPED
• ...
• 00:05 - File 50 uploaded → SKIPPED

Result: User receives 1 email about File 1, never learns about files 2-50

Proposal

• 00:00 - File 1 uploaded → Email sent ✓
• 00:01 - File 2 uploaded → Queued
• 00:02 - File 3 uploaded → Queued
• ...
• 00:30 - Interval expires → Digest email with files 2-50 ✓

Result: User receives 2 emails - immediate + digest with all files listed

type Properties struct {
      // ...

      Aggregate      bool   `json:"aggregate,omitempty"`       // Enable email aggregation
      DigestTemplate string `json:"digest_template,omitempty"` // Template for digest email
  }

type Notification struct {
      // ...

      // Status: "sent" (default), "pending" (queued for digest), "aggregated"
      Status string `json:"status,omitempty"`
  }

NotificationSharingFileChanged: {
      Description:    "Notify about new files in sharings",
      Collapsible:    false,
      Aggregate:      true,
      MinInterval:    5 * time.Minute,
      MailTemplate:   "sharing_file_changed",         // Single file email
      DigestTemplate: "sharing_file_changed_digest",  // Aggregated email
      Aggregator:     aggregateSharingFileChanges,
  },
func aggregateFileChanges(notifs []*notification.Notification) map[string]interface{} {
      // ... aggregation logic
 }