Fix controlled document ID allocation

[ArtyomSavchenko]

Summary
This PR fixes controlled document and template code handling during creation and workspace export.
Custom IDs such as TESTTMP-1 are now preserved during export when available, instead of being replaced with generated default codes such as TMPL-2.

Changes

• Added a reusable identifier allocator in @hcengineering/core.
• Added atomic identifier reservations backed by server-side transaction conditions.
• Prevented duplicate IDs during concurrent allocation requests.
• Supported preserving a requested custom numeric code even when the current sequence is higher.
• Incremented to the next available code when the requested one is already occupied.
• Updated controlled document and template creation to use the shared allocator.
• Updated export mapping to preserve custom codes and resolve conflicts through the allocator.
• Added migration logic to reserve identifiers of existing controlled documents.
• Unified identifier parsing and added support for prefixes containing hyphens.
• Removed obsolete client-side conflict-checking logic from the create-document UI.