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/handlers/user_handler.go

@@ -4,9 +4,9 @@ import (
 	"net/http"
 	"strconv"
 
-	"github.com/gin-gonic/gin"
+	"github.com/labstack/echo/v4"
 
-	"github.com/treytartt/casera-api/internal/i18n"
+	"github.com/treytartt/casera-api/internal/apperrors"
 	"github.com/treytartt/casera-api/internal/middleware"
 	"github.com/treytartt/casera-api/internal/models"
 	"github.com/treytartt/casera-api/internal/services"
@@ -25,58 +25,50 @@ func NewUserHandler(userService *services.UserService) *UserHandler {
 }
 
 // ListUsers handles GET /api/users/
-func (h *UserHandler) ListUsers(c *gin.Context) {
-	user := c.MustGet(middleware.AuthUserKey).(*models.User)
+func (h *UserHandler) ListUsers(c echo.Context) error {
+	user := c.Get(middleware.AuthUserKey).(*models.User)
 
 	// Only allow listing users that share residences with the current user
 	users, err := h.userService.ListUsersInSharedResidences(user.ID)
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
-		return
+		return err
 	}
 
-	c.JSON(http.StatusOK, gin.H{
+	return c.JSON(http.StatusOK, map[string]interface{}{
 		"count":   len(users),
 		"results": users,
 	})
 }
 
 // GetUser handles GET /api/users/:id/
-func (h *UserHandler) GetUser(c *gin.Context) {
-	user := c.MustGet(middleware.AuthUserKey).(*models.User)
+func (h *UserHandler) GetUser(c echo.Context) error {
+	user := c.Get(middleware.AuthUserKey).(*models.User)
 
 	userID, err := strconv.ParseUint(c.Param("id"), 10, 32)
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": i18n.LocalizedMessage(c, "error.invalid_user_id")})
-		return
+		return apperrors.BadRequest("error.invalid_user_id")
 	}
 
 	// Can only view users that share a residence
 	targetUser, err := h.userService.GetUserIfSharedResidence(uint(userID), user.ID)
 	if err != nil {
-		if err == services.ErrUserNotFound {
-			c.JSON(http.StatusNotFound, gin.H{"error": i18n.LocalizedMessage(c, "error.user_not_found")})
-			return
-		}
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
-		return
+		return err
 	}
 
-	c.JSON(http.StatusOK, targetUser)
+	return c.JSON(http.StatusOK, targetUser)
 }
 
 // ListProfiles handles GET /api/users/profiles/
-func (h *UserHandler) ListProfiles(c *gin.Context) {
-	user := c.MustGet(middleware.AuthUserKey).(*models.User)
+func (h *UserHandler) ListProfiles(c echo.Context) error {
+	user := c.Get(middleware.AuthUserKey).(*models.User)
 
 	// List profiles of users in shared residences
 	profiles, err := h.userService.ListProfilesInSharedResidences(user.ID)
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
-		return
+		return err
 	}
 
-	c.JSON(http.StatusOK, gin.H{
+	return c.JSON(http.StatusOK, map[string]interface{}{
 		"count":   len(profiles),
 		"results": profiles,
 	})