[PierreRaybaut]

Stacked on #374.

When a method cannot run because metadata are missing, DataLab now leads users to the tool that sets them:

• The status of the method ends with "To set it, use Edit > Metadata > Add metadata...".
• The Known keys list of Add metadata also offers the keys expected by the methods of the active application plugins (for the signal or image panel), after the keys found on the selected objects.
• The catalog re-assesses the methods when objects are modified (SIG_OBJECT_MODIFIED), not only when the selection changes, so the status follows metadata edits immediately.

Tests

• datalab/tests/features/plugins, Add metadata and welcome tests: 92 passed, with new tests for the declared keys (function and panel hook), the hint, and the refresh on object modification.

Docs: overview, signal/image menu_edit pages and 1.4 release notes, with their French catalogs; datalab.po updated.

Assisted-by: Claude Opus 5.5