Add performance optimizations and database indexes

Database Indexes (migrations 006-009):
- Add case-insensitive indexes for auth lookups (email, username)
- Add composite indexes for task kanban queries
- Add indexes for notification, document, and completion queries
- Add unique index for active share codes
- Remove redundant idx_share_code_active and idx_notification_user_sent

Repository Optimizations:
- Add FindResidenceIDsByUser() lightweight method (IDs only, no preloads)
- Optimize GetResidenceUsers() with single UNION query (was 2 queries)
- Optimize kanban completion preloads to minimal columns (id, task_id, completed_at)

Service Optimizations:
- Remove Category/Priority/Frequency preloads from task queries
- Remove summary calculations from CRUD responses (client calculates)
- Use lightweight FindResidenceIDsByUser() instead of full FindByUser()

These changes reduce database load and response times for common operations.

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

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

internal/services/task_service_test.go

@@ -76,8 +76,10 @@ func TestTaskService_CreateTask_WithOptionalFields(t *testing.T) {
 
 	resp, err := service.CreateTask(req, user.ID)
 	require.NoError(t, err)
-	assert.NotNil(t, resp.Data.Category)
-	assert.NotNil(t, resp.Data.Priority)
+	// Note: Category and Priority are no longer preloaded for performance
+	// Client resolves from cache using CategoryID and PriorityID
+	assert.NotNil(t, resp.Data.CategoryID, "CategoryID should be set")
+	assert.NotNil(t, resp.Data.PriorityID, "PriorityID should be set")
 	assert.NotNil(t, resp.Data.DueDate)
 	assert.NotNil(t, resp.Data.EstimatedCost)
 }
@@ -149,7 +151,7 @@ func TestTaskService_ListTasks(t *testing.T) {
 	testutil.CreateTestTask(t, db, residence.ID, user.ID, "Task 2")
 	testutil.CreateTestTask(t, db, residence.ID, user.ID, "Task 3")
 
-	resp, err := service.ListTasks(user.ID)
+	resp, err := service.ListTasks(user.ID, time.Now().UTC())
 	require.NoError(t, err)
 	// ListTasks returns a KanbanBoardResponse with columns
 	// Count total tasks across all columns