feat(planning): #62 #63 #64 enhance leave planner with calculation date and entitlement details

- Introduced calculationDate in various service interfaces and snapshots to track the date of planning calculations.
- Added futureEntitlement and includedEntitlement fields to the translation service and respective language files for better user feedback.
- Updated leave-planner.worker to handle calculationDate and declaredDays in requests.
- Enhanced tests to ensure proper handling of calculation dates and artifact retention during planning processes.
- Improved snapshot and explanation outputs to include calculation date for clarity in planning results.

src/i18n/de.json

@@ -127,6 +127,9 @@
 		}
 	},
 	"planning": {
+		"calculationDate": "Berechnungsdatum",
+		"futureEntitlement": "Erzeugter künftiger Anspruch",
+		"includedEntitlement": "Anspruch bereits in den gemeldeten Guthaben enthalten",
 		"title": "Ihr optimiertes Jahr",
 		"daysPlaced": "Eingeplante Urlaubstage",
 		"daysGained": "Gewonnene arbeitsfreie Tage",