feat: add metadata API tools and availability test (#59)

Add new MCP tools for:
- Labels (CRUD operations)
- States (CRUD operations)
- Pages (workspace and project pages)
- Work item activities (list/retrieve)
- Work item comments (CRUD operations)
- Work item links (CRUD operations)
- Work item relations (list/create/remove)
- Work item types (CRUD operations)
- Work logs (CRUD operations)
- Workspaces (members, features)

Also add test_tools_availability() integration test to verify all 95
expected tools are registered after releases.

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

* fix: use correct nested SDK API paths for work item sub-resources

Fix API access patterns to use client.work_items.* instead of
client.work_item_* for nested sub-resources:
- work_logs -> work_items.work_logs
- activities -> work_items.activities
- comments -> work_items.comments
- links -> work_items.links
- relations -> work_items.relations

* fix: type and enum validations