feat(applications): guide users to set the metadata methods expect

[PierreRaybaut]

Stacked on #21.

When a method cannot run because metadata are missing, DataLab-Web 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 (dlw_plugins.declared_metadata_keys), after the keys found on the selected objects.
• The Applications window re-assesses the methods after every workspace mutation while it is open, so the status follows metadata edits immediately.
• Long choices such as plugin keys no longer widen parameter dialogs (.dataset-form-control { min-width: 0 }).

Tests

• Vitest: 740 passed (new test for the re-assessment and the hint); pytest: 359 passed (new test for the declared keys). Prettier, ESLint, tsc and i18n:check pass.
• Playwright: 15 form, dialog-bridge and application specs pass. A throwaway probe checked the live flow with the Camera quickstart: removing exposure_time_s from a flat frame turns the method from ready to not ready with the hint, Known keys lists the Camera keys, and the list stays within the dialog.

Assisted-by: Claude Opus 5.5