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/echohelpers/helpers.go

@@ -0,0 +1,45 @@
+package echohelpers
+
+import (
+	"strconv"
+
+	"github.com/labstack/echo/v4"
+)
+
+// DefaultQuery returns query param with default if not present
+func DefaultQuery(c echo.Context, key, defaultValue string) string {
+	val := c.QueryParam(key)
+	if val == "" {
+		return defaultValue
+	}
+	return val
+}
+
+// ParseUintParam parses a path parameter as uint
+func ParseUintParam(c echo.Context, name string) (uint, error) {
+	val, err := strconv.ParseUint(c.Param(name), 10, 32)
+	if err != nil {
+		return 0, err
+	}
+	return uint(val), nil
+}
+
+// ParseIntParam parses a path parameter as int
+func ParseIntParam(c echo.Context, name string) (int, error) {
+	val, err := strconv.Atoi(c.Param(name))
+	if err != nil {
+		return 0, err
+	}
+	return val, nil
+}
+
+// BindAndValidate binds and validates the request body
+func BindAndValidate(c echo.Context, req interface{}) error {
+	if err := c.Bind(req); err != nil {
+		return err
+	}
+	if err := c.Validate(req); err != nil {
+		return err
+	}
+	return nil
+}