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/handlers/task_handler_test.go

@@ -100,8 +100,10 @@ func TestTaskHandler_CreateTask(t *testing.T) {
 
 		taskData := response["data"].(map[string]interface{})
 		assert.Equal(t, "Install new lights", taskData["title"])
-		assert.NotNil(t, taskData["category"])
-		assert.NotNil(t, taskData["priority"])
+		// Note: Category and Priority are no longer preloaded for performance
+		// Client resolves from cache using category_id and priority_id
+		assert.NotNil(t, taskData["category_id"], "category_id should be set")
+		assert.NotNil(t, taskData["priority_id"], "priority_id should be set")
 		assert.Equal(t, "150.5", taskData["estimated_cost"]) // Decimal serializes as string
 	})