Migrate from Gin to Echo framework and add comprehensive integration tests

Major changes:
- Migrate all handlers from Gin to Echo framework
- Add new apperrors, echohelpers, and validator packages
- Update middleware for Echo compatibility
- Add ArchivedHandler to task categorization chain (archived tasks go to cancelled_tasks column)
- Add 6 new integration tests:
  - RecurringTaskLifecycle: NextDueDate advancement for weekly/monthly tasks
  - MultiUserSharing: Complex sharing with user removal
  - TaskStateTransitions: All state transitions and kanban column changes
  - DateBoundaryEdgeCases: Threshold boundary testing
  - CascadeOperations: Residence deletion cascade effects
  - MultiUserOperations: Shared residence collaboration
- Add single-purpose repository functions for kanban columns (GetOverdueTasks, GetDueSoonTasks, etc.)
- Fix RemoveUser route param mismatch (userId -> user_id)
- Fix determineExpectedColumn helper to correctly prioritize in_progress over overdue

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/testutil/testutil.go

@@ -8,14 +8,16 @@ import (
 	"sync"
 	"testing"
 
-	"github.com/gin-gonic/gin"
+	"github.com/labstack/echo/v4"
 	"github.com/stretchr/testify/require"
 	"gorm.io/driver/sqlite"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
 
+	"github.com/treytartt/casera-api/internal/apperrors"
 	"github.com/treytartt/casera-api/internal/i18n"
 	"github.com/treytartt/casera-api/internal/models"
+	"github.com/treytartt/casera-api/internal/validator"
 )
 
 var i18nOnce sync.Once
@@ -68,14 +70,16 @@ func SetupTestDB(t *testing.T) *gorm.DB {
 	return db
 }
 
-// SetupTestRouter creates a test Gin router
-func SetupTestRouter() *gin.Engine {
-	gin.SetMode(gin.TestMode)
-	return gin.New()
+// SetupTestRouter creates a test Echo router with the custom error handler
+func SetupTestRouter() *echo.Echo {
+	e := echo.New()
+	e.Validator = validator.NewCustomValidator()
+	e.HTTPErrorHandler = apperrors.HTTPErrorHandler
+	return e
 }
 
 // MakeRequest makes a test HTTP request and returns the response
-func MakeRequest(router *gin.Engine, method, path string, body interface{}, token string) *httptest.ResponseRecorder {
+func MakeRequest(router *echo.Echo, method, path string, body interface{}, token string) *httptest.ResponseRecorder {
 	var reqBody *bytes.Buffer
 	if body != nil {
 		jsonBody, _ := json.Marshal(body)
@@ -90,9 +94,9 @@ func MakeRequest(router *gin.Engine, method, path string, body interface{}, toke
 		req.Header.Set("Authorization", "Token "+token)
 	}
 
-	w := httptest.NewRecorder()
-	router.ServeHTTP(w, req)
-	return w
+	rec := httptest.NewRecorder()
+	router.ServeHTTP(rec, req)
+	return rec
 }
 
 // ParseJSON parses JSON response body into a map
@@ -287,11 +291,13 @@ func AssertStatusCode(t *testing.T, w *httptest.ResponseRecorder, expected int)
 }
 
 // MockAuthMiddleware creates middleware that sets a test user in context
-func MockAuthMiddleware(user *models.User) gin.HandlerFunc {
-	return func(c *gin.Context) {
-		c.Set("auth_user", user)
-		c.Set("auth_token", "test-token")
-		c.Next()
+func MockAuthMiddleware(user *models.User) echo.MiddlewareFunc {
+	return func(next echo.HandlerFunc) echo.HandlerFunc {
+		return func(c echo.Context) error {
+			c.Set("auth_user", user)
+			c.Set("auth_token", "test-token")
+			return next(c)
+		}
 	}
 }
 
@@ -329,3 +335,22 @@ func CreateTestDocument(t *testing.T, db *gorm.DB, residenceID, createdByID uint
 	require.NoError(t, err)
 	return doc
 }
+
+// AssertAppError asserts that an error is an AppError with a specific status code and message key
+func AssertAppError(t *testing.T, err error, expectedCode int, expectedMessageKey string) {
+	require.Error(t, err, "expected an error")
+
+	var appErr *apperrors.AppError
+	require.ErrorAs(t, err, &appErr, "expected an AppError")
+	require.Equal(t, expectedCode, appErr.Code, "unexpected status code")
+	require.Equal(t, expectedMessageKey, appErr.MessageKey, "unexpected message key")
+}
+
+// AssertAppErrorCode asserts that an error is an AppError with a specific status code
+func AssertAppErrorCode(t *testing.T, err error, expectedCode int) {
+	require.Error(t, err, "expected an error")
+
+	var appErr *apperrors.AppError
+	require.ErrorAs(t, err, &appErr, "expected an AppError")
+	require.Equal(t, expectedCode, appErr.Code, "unexpected status code")
+}