feat(#10548): add shared document type constants

[kumaranurag00748-byte]

Description

Adds shared DOC_TYPES constants for the following document types:

• DOC_TYPES.TASK
• DOC_TYPES.TARGET
• DOC_TYPES.USER_SETTINGS

Replaces persisted document-type literals for task, target, and user-settings across API, webapp, rules-engine, datasource, and user-management code. This keeps document type values unchanged while removing duplicated magic strings.

Closes #10548

Code review checklist

• UI/UX backwards compatible: Test it works for the new design (enabled by default). And test it works in the old design, enable can_view_old_navigation permission to see the old design. Test it has appropriate design for RTL languages.
• Readable: Concise, well named, follows the style guide
• Documented: Configuration and user documentation on cht-docs
• Tested: Unit and/or e2e where appropriate
• Internationalised: All user facing text
• Backwards compatible: Existing persisted values remain unchanged; this change only replaces duplicated literals with shared constants.
• AI disclosure: AI assistance was used to locate relevant usages, implement the constant replacements, and validate the changes.

Validation

• Rules-engine tests: 224 passing
• User-management tests: 178 passing
• ESLint passed for all changed source files
• Runtime verification confirmed:
  • DOC_TYPES.TASK === 'task'
  • DOC_TYPES.TARGET === 'target'
  • DOC_TYPES.USER_SETTINGS === 'user-settings'
• git diff --check passed

Full CouchDB-backed integration tests were not run because Docker/CouchDB was unavailable in the local environment.

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.