Add Google Tasks integration (#43)

- New GoogleTasksClient for fetching and managing Google Tasks
- Tasks appear in Timeline view with yellow indicator dot
- Tap checkbox to complete/uncomplete tasks via Google API
- Shares credentials file with Google Calendar (GOOGLE_CREDENTIALS_FILE)
- Configure task list via GOOGLE_TASKS_LIST_ID env var (default: @default)
- Supports comma-separated list IDs for multiple lists

New files:
- internal/api/google_tasks.go - Google Tasks API client

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

1 files changed, 28 insertions, 1 deletions

diff --git a/internal/handlers/timeline_logic.go b/internal/handlers/timeline_logic.go
index 553593d..5ea44b5 100644
--- a/internal/handlers/timeline_logic.go
+++ b/internal/handlers/timeline_logic.go
@@ -13,7 +13,7 @@ import (
 )
 
 // BuildTimeline aggregates and normalizes data into a timeline structure
-func BuildTimeline(ctx context.Context, s *store.Store, calendarClient api.GoogleCalendarAPI, start, end time.Time) ([]models.TimelineItem, error) {
+func BuildTimeline(ctx context.Context, s *store.Store, calendarClient api.GoogleCalendarAPI, tasksClient api.GoogleTasksAPI, start, end time.Time) ([]models.TimelineItem, error) {
 	var items []models.TimelineItem
 	now := config.Now()
 
@@ -151,6 +151,33 @@ func BuildTimeline(ctx context.Context, s *store.Store, calendarClient api.Googl
 		}
 	}
 
+	// 5. Fetch Google Tasks
+	if tasksClient != nil {
+		gTasks, err := tasksClient.GetTasksByDateRange(ctx, start, end)
+		if err == nil {
+			for _, gTask := range gTasks {
+				taskTime := start // Default to start of range if no due date
+				if gTask.DueDate != nil {
+					taskTime = *gTask.DueDate
+				}
+				item := models.TimelineItem{
+					ID:           gTask.ID,
+					Type:         models.TimelineItemTypeGTask,
+					Title:        gTask.Title,
+					Time:         taskTime,
+					Description:  gTask.Notes,
+					URL:          gTask.URL,
+					OriginalItem: gTask,
+					IsCompleted:  gTask.Completed,
+					Source:       "gtasks",
+					ListID:       gTask.ListID,
+				}
+				item.ComputeDaySection(now)
+				items = append(items, item)
+			}
+		}
+	}
+
 	// Sort items by Time
 	sort.Slice(items, func(i, j int) bool {
 		return items[i].Time.Before(items[j].Time)