fix: prevent modifications to transmitted edocuments

[maasanto]

Once an EDocument reaches a terminal state (Transmission Successful, Transmission Failed, Matching Successful, Matching Failed), it should be treated as immutable.

Without this fix, before_save re-runs XML validation on every save, which resets the status back to Validation Successful — re-enabling the Send button on an already-transmitted document. Additionally, the status field was editable by users, allowing manual overrides of system-managed state.

Changes

Server-side (edocument.py):

• generate_xml() and validate_xml() now throw if status is Transmission Successful
• before_save skips automatic re-validation for documents in terminal statuses

Client-side (edocument.js):

• Hides "Generate XML" and "Validate XML" buttons for transmitted documents

DocType definition (edocument.json):

• status field is now read_only — it is entirely system-managed (set by validation, matching, and transmission logic), so users should not be able to manually override it