Add timezone-aware daily digest notifications

The daily digest notification count was inconsistent with the kanban UI
because the server used UTC time while the client used local time.
A task due Dec 24 would appear overdue on the server (UTC Dec 25) but
still show as "due today" for the user (local Dec 24).

Changes:
- Add timezone column to notification_preference table
- Auto-capture user's timezone from X-Timezone header when fetching tasks
- Use stored timezone in HandleDailyDigest for accurate overdue calculation

The mobile app already sends X-Timezone on every request, so no client
changes are needed. The timezone is captured on each app launch when
the tasks API is called.

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

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

internal/handlers/task_handler.go

@@ -36,6 +36,12 @@ func (h *TaskHandler) ListTasks(c echo.Context) error {
 	user := c.Get(middleware.AuthUserKey).(*models.User)
 	userNow := middleware.GetUserNow(c)
 
+	// Auto-capture timezone from header for background job calculations (e.g., daily digest)
+	// This runs in a goroutine to avoid blocking the response
+	if tzHeader := c.Request().Header.Get("X-Timezone"); tzHeader != "" {
+		go h.taskService.UpdateUserTimezone(user.ID, tzHeader)
+	}
+
 	response, err := h.taskService.ListTasks(user.ID, userNow)
 	if err != nil {
 		return err

internal/models/notification.go

@@ -33,6 +33,10 @@ type NotificationPreference struct {
 	TaskOverdueHour      *int `gorm:"column:task_overdue_hour" json:"task_overdue_hour"`
 	WarrantyExpiringHour *int `gorm:"column:warranty_expiring_hour" json:"warranty_expiring_hour"`
 	DailyDigestHour      *int `gorm:"column:daily_digest_hour" json:"daily_digest_hour"`
+
+	// User timezone for background job calculations (IANA name, e.g., "America/Los_Angeles")
+	// Auto-captured from X-Timezone header on API calls
+	Timezone *string `gorm:"column:timezone;type:varchar(50)" json:"timezone"`
 }
 
 // TableName returns the table name for GORM

internal/services/notification_service.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"errors"
 	"strconv"
+	"time"
 
 	"gorm.io/gorm"
 
@@ -237,6 +238,28 @@ func (s *NotificationService) UpdatePreferences(userID uint, req *UpdatePreferen
 	return NewNotificationPreferencesResponse(prefs), nil
 }
 
+// UpdateUserTimezone updates the user's timezone for background job calculations.
+// This is called automatically when the user makes API calls (e.g., fetching tasks).
+// The timezone should be an IANA timezone name (e.g., "America/Los_Angeles").
+func (s *NotificationService) UpdateUserTimezone(userID uint, timezone string) {
+	// Validate timezone is a valid IANA name
+	if _, err := time.LoadLocation(timezone); err != nil {
+		return // Invalid timezone, skip silently
+	}
+
+	// Get or create preferences and update timezone
+	prefs, err := s.notificationRepo.GetOrCreatePreferences(userID)
+	if err != nil {
+		return // Skip silently on error
+	}
+
+	// Only update if timezone changed (avoid unnecessary DB writes)
+	if prefs.Timezone == nil || *prefs.Timezone != timezone {
+		prefs.Timezone = &timezone
+		_ = s.notificationRepo.UpdatePreferences(prefs)
+	}
+}
+
 // === Device Registration ===
 
 // RegisterDevice registers a device for push notifications

internal/services/task_service.go

@@ -996,3 +996,14 @@ func (s *TaskService) GetFrequencies() ([]responses.TaskFrequencyResponse, error
 	}
 	return result, nil
 }
+
+// === Timezone ===
+
+// UpdateUserTimezone updates the user's timezone for background job calculations.
+// This is called from handlers when the X-Timezone header is present.
+// Delegates to NotificationService since timezone is stored in notification preferences.
+func (s *TaskService) UpdateUserTimezone(userID uint, timezone string) {
+	if s.notificationService != nil {
+		s.notificationService.UpdateUserTimezone(userID, timezone)
+	}
+}

internal/worker/jobs/handler.go

@@ -319,6 +319,23 @@ func (h *Handler) HandleDailyDigest(ctx context.Context, task *asynq.Task) error
 	var usersNotified int
 
 	for _, userID := range eligibleUserIDs {
+		// Get user's timezone from notification preferences for accurate overdue calculation
+		// This ensures the daily digest matches what the user sees in the kanban UI
+		var userNow time.Time
+		var prefs models.NotificationPreference
+		if err := h.db.Where("user_id = ?", userID).First(&prefs).Error; err == nil && prefs.Timezone != nil {
+			if loc, err := time.LoadLocation(*prefs.Timezone); err == nil {
+				// Use start of day in user's timezone (matches kanban behavior)
+				userNowInTz := time.Now().In(loc)
+				userNow = time.Date(userNowInTz.Year(), userNowInTz.Month(), userNowInTz.Day(), 0, 0, 0, 0, loc)
+				log.Debug().Uint("user_id", userID).Str("timezone", *prefs.Timezone).Time("user_now", userNow).Msg("Using user timezone for daily digest")
+			} else {
+				userNow = now // Fallback to UTC
+			}
+		} else {
+			userNow = now // Fallback to UTC if no timezone stored
+		}
+
 		// Get user's residence IDs (owned + member)
 		residenceIDs, err := h.residenceRepo.FindResidenceIDsByUser(userID)
 		if err != nil {
@@ -331,20 +348,21 @@ func (h *Handler) HandleDailyDigest(ctx context.Context, task *asynq.Task) error
 		}
 
 		// Query overdue tasks using canonical scopes (excludes in-progress)
+		// Uses userNow (timezone-aware) for accurate overdue detection
 		opts := repositories.TaskFilterOptions{
 			ResidenceIDs:       residenceIDs,
 			IncludeInProgress:  false, // Match kanban: in-progress tasks not in overdue column
 			PreloadCompletions: true,
 		}
 
-		overdueTasks, err := h.taskRepo.GetOverdueTasks(now, opts)
+		overdueTasks, err := h.taskRepo.GetOverdueTasks(userNow, opts)
 		if err != nil {
 			log.Error().Err(err).Uint("user_id", userID).Msg("Failed to get overdue tasks")
 			continue
 		}
 
 		// Query due-this-week tasks (7 days threshold)
-		dueSoonTasks, err := h.taskRepo.GetDueSoonTasks(now, 7, opts)
+		dueSoonTasks, err := h.taskRepo.GetDueSoonTasks(userNow, 7, opts)
 		if err != nil {
 			log.Error().Err(err).Uint("user_id", userID).Msg("Failed to get due-soon tasks")
 			continue