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/task/task.go

@@ -109,9 +109,10 @@ func HasCompletions(task *models.Task) bool {
 	return predicates.HasCompletions(task)
 }
 
-// CompletionCount returns the number of completions for a task.
-func CompletionCount(task *models.Task) int {
-	return predicates.CompletionCount(task)
+// GetCompletionCount returns the number of completions for a task.
+// Supports both preloaded Completions slice and computed CompletionCount field.
+func GetCompletionCount(task *models.Task) int {
+	return predicates.GetCompletionCount(task)
 }
 
 // IsRecurring returns true if the task has a recurring frequency.