CR-96:Changes to '+ Add Document' button

[don-aot]

Summary:

Addresses user testing feedback where users were confused by the lack of an "Add Document" button on the document list screen. The button now appears in the header of the Certificate and Amendments (and Other Orders) screens.

Changes:

• Added "Add Document" button to the Documents screen header
• Button is context-aware — document types are filtered to only those belonging to the current shell (e.g. "Other Order" is not available when in the Certificate and Amendments shell)
• Pre-populates the project in the modal since the user is already in a project context
• CreateDocumentModal extended with preselectedProject and restrictToCategoryId props to support this behaviour without duplicating logic