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/tracking_handler.go

@@ -4,7 +4,7 @@ import (
 	"encoding/base64"
 	"net/http"
 
-	"github.com/gin-gonic/gin"
+	"github.com/labstack/echo/v4"
 
 	"github.com/treytartt/casera-api/internal/services"
 )
@@ -26,7 +26,7 @@ var transparentGIF, _ = base64.StdEncoding.DecodeString("R0lGODlhAQABAIAAAAAAAP/
 
 // TrackEmailOpen handles email open tracking via tracking pixel
 // GET /api/track/open/:trackingID
-func (h *TrackingHandler) TrackEmailOpen(c *gin.Context) {
+func (h *TrackingHandler) TrackEmailOpen(c echo.Context) error {
 	trackingID := c.Param("trackingID")
 
 	if trackingID != "" && h.onboardingService != nil {
@@ -37,9 +37,9 @@ func (h *TrackingHandler) TrackEmailOpen(c *gin.Context) {
 	}
 
 	// Return 1x1 transparent GIF
-	c.Header("Content-Type", "image/gif")
-	c.Header("Cache-Control", "no-store, no-cache, must-revalidate, proxy-revalidate")
-	c.Header("Pragma", "no-cache")
-	c.Header("Expires", "0")
-	c.Data(http.StatusOK, "image/gif", transparentGIF)
+	c.Response().Header().Set("Content-Type", "image/gif")
+	c.Response().Header().Set("Cache-Control", "no-store, no-cache, must-revalidate, proxy-revalidate")
+	c.Response().Header().Set("Pragma", "no-cache")
+	c.Response().Header().Set("Expires", "0")
+	return c.Blob(http.StatusOK, "image/gif", transparentGIF)
 }