Add webhook logging, pagination, middleware, migrations, and prod hardening

- Webhook event logging repo and subscription webhook idempotency
- Pagination helper (echohelpers) with cursor/offset support
- Request ID and structured logging middleware
- Push client improvements (FCM HTTP v1, better error handling)
- Task model version column, business constraint migrations, targeted indexes
- Expanded categorization chain tests
- Email service and config hardening
- CI workflow updates, .gitignore additions, .env.example updates

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

internal/repositories/webhook_event_repo.go

@@ -0,0 +1,54 @@
+package repositories
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// WebhookEvent represents a processed webhook event for deduplication
+type WebhookEvent struct {
+	ID          uint      `gorm:"primaryKey"`
+	EventID     string    `gorm:"column:event_id;size:255;not null;uniqueIndex:idx_provider_event_id"`
+	Provider    string    `gorm:"column:provider;size:20;not null;uniqueIndex:idx_provider_event_id"`
+	EventType   string    `gorm:"column:event_type;size:100;not null"`
+	ProcessedAt time.Time `gorm:"column:processed_at;autoCreateTime"`
+	PayloadHash string    `gorm:"column:payload_hash;size:64"`
+}
+
+func (WebhookEvent) TableName() string {
+	return "webhook_event_log"
+}
+
+// WebhookEventRepository handles webhook event deduplication
+type WebhookEventRepository struct {
+	db *gorm.DB
+}
+
+// NewWebhookEventRepository creates a new webhook event repository
+func NewWebhookEventRepository(db *gorm.DB) *WebhookEventRepository {
+	return &WebhookEventRepository{db: db}
+}
+
+// HasProcessed checks if an event has already been processed
+func (r *WebhookEventRepository) HasProcessed(provider, eventID string) (bool, error) {
+	var count int64
+	err := r.db.Model(&WebhookEvent{}).
+		Where("provider = ? AND event_id = ?", provider, eventID).
+		Count(&count).Error
+	if err != nil {
+		return false, err
+	}
+	return count > 0, nil
+}
+
+// RecordEvent records a processed webhook event
+func (r *WebhookEventRepository) RecordEvent(provider, eventID, eventType, payloadHash string) error {
+	event := &WebhookEvent{
+		EventID:     eventID,
+		Provider:    provider,
+		EventType:   eventType,
+		PayloadHash: payloadHash,
+	}
+	return r.db.Create(event).Error
+}