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>

migrations/008_additional_performance_indexes.up.sql

@@ -0,0 +1,47 @@
+-- Additional performance optimization indexes
+-- Migration: 008_additional_performance_indexes
+
+-- =====================================================
+-- KANBAN QUERY OPTIMIZATION
+-- =====================================================
+
+-- Composite index for kanban board queries
+-- Covers: WHERE residence_id IN ? AND is_archived = false
+-- with ordering by due_date, next_due_date
+CREATE INDEX IF NOT EXISTS idx_task_kanban_composite
+    ON task_task (residence_id, is_archived, is_cancelled, next_due_date, due_date)
+    WHERE is_archived = false;
+
+-- =====================================================
+-- COMPLETION QUERY OPTIMIZATION
+-- =====================================================
+
+-- Ordering index for completion queries (most recent first)
+CREATE INDEX IF NOT EXISTS idx_completion_task_date
+    ON task_taskcompletion (task_id, completed_at DESC);
+
+-- =====================================================
+-- SHARE CODE OPTIMIZATION
+-- =====================================================
+
+-- Unique index for active share code lookups
+CREATE UNIQUE INDEX IF NOT EXISTS idx_sharecode_code_active
+    ON residence_residencesharecode (code)
+    WHERE is_active = true;
+
+-- =====================================================
+-- RESIDENCE USER ACCESS OPTIMIZATION
+-- =====================================================
+
+-- Index for residence user membership queries (used by FindResidenceIDsByUser)
+CREATE INDEX IF NOT EXISTS idx_residence_users_user_residence
+    ON residence_residence_users (user_id, residence_id);
+
+-- =====================================================
+-- TASK IN_PROGRESS QUERIES
+-- =====================================================
+
+-- Index for in_progress task queries (kanban "In Progress" column)
+CREATE INDEX IF NOT EXISTS idx_task_in_progress
+    ON task_task (residence_id, in_progress)
+    WHERE in_progress = true AND is_cancelled = false AND is_archived = false;