feat: add test data cleanup endpoint

Add POST /maintenance/cleanup/test-data endpoint to purge LLM test data
from wiki, graph, and vectors. Security-restricted to test user namespace
only (users/llm-tester/*, users/llm_tester/*).

- Supports dry_run=true (default) to preview before deleting
- Cleans vectors, graph nodes, and wiki pages
- Scheduler task configured for weekly cleanup (Sunday 3:00 AM)

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

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

CHANGELOG.md

@@ -5,6 +5,16 @@ All notable changes to Library Desk will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.4.4] - 2025-12-24
+
+### Added
+
+- **Test Data Cleanup Endpoint** - `POST /maintenance/cleanup/test-data`
+  - Purges LLM test data from wiki, graph, and vectors
+  - Security-restricted to test user namespace only (`users/llm-tester/*`, `users/llm_tester/*`)
+  - Supports `dry_run=true` (default) to preview before deleting
+  - Scheduler task configured for weekly cleanup (Sunday 3:00 AM)
+
 ## [1.4.3] - 2025-12-24
 
 ### Changed