fix(auth): resolve compile errors in timezone update handler

The timezone update block in UpdateProfile() referenced undefined
variables ctx and userUUID, causing a compile error. Fixed to use
c.Request().Context() and targetUserUUID which are the correct
variables in that handler scope.

Also added Timezone field to AdminUpdateUserRequest struct so the
timezone value is properly bound from JSON requests, since
UpdateProfile() binds to AdminUpdateUserRequest rather than
UpdateProfileRequest.

internal/handlers/auth.go

@@ -96,6 +96,7 @@ type AdminUpdateUserRequest struct {
 	FirstName string `json:"first_name,omitempty" validate:"omitempty,max=100"`
 	LastName  string `json:"last_name,omitempty" validate:"omitempty,max=100"`
 	Theme     string `json:"theme,omitempty" validate:"omitempty"`
+	Timezone  string `json:"timezone,omitempty" validate:"omitempty"`
 	Role      string `json:"role,omitempty" validate:"omitempty,oneof=user admin"`
 }
 
@@ -572,8 +573,8 @@ func (h *AuthHandler) UpdateProfile(c *echo.Context) error {
 				"error": "Invalid timezone",
 			})
 		}
-		err := h.db.UpdateUserTimezone(ctx, database.UpdateUserTimezoneParams{
-			ID:       pgtype.UUID{Bytes: userUUID, Valid: true},
+		err := h.db.UpdateUserTimezone(c.Request().Context(), database.UpdateUserTimezoneParams{
+			ID:       targetUserUUID,
 			Timezone: pgtype.Text{String: req.Timezone, Valid: true},
 		})
 		if err != nil {