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/handlers/task_handler_test.go

@@ -358,7 +358,7 @@ func TestTaskHandler_UncancelTask(t *testing.T) {
 
 	// Cancel first
 	taskRepo := repositories.NewTaskRepository(db)
-	taskRepo.Cancel(task.ID)
+	taskRepo.Cancel(task.ID, task.Version)
 
 	authGroup := e.Group("/api/tasks")
 	authGroup.Use(testutil.MockAuthMiddleware(user))
@@ -418,7 +418,7 @@ func TestTaskHandler_UnarchiveTask(t *testing.T) {
 
 	// Archive first
 	taskRepo := repositories.NewTaskRepository(db)
-	taskRepo.Archive(task.ID)
+	taskRepo.Archive(task.ID, task.Version)
 
 	authGroup := e.Group("/api/tasks")
 	authGroup.Use(testutil.MockAuthMiddleware(user))