Give the analytics overview a per-parent, per-year balance series

Each parent projection now carries one entry per calendar year from
birth to the fourth birthday: vacation earned, carried in, planned,
left, carried out and expiring under Semesterlagen's 20-day floor and
5-year carry-over, plus parental-leave days used and left at year end
with the age-4 clamp applied in the birthday year. The overview sums
them into per-year totals. Frontend types, mapper and fixtures follow.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XBRLomdLK9jF7wU7a8AA6H

backend/scripts/seed_demo.py

@@ -118,7 +118,9 @@ def _build_services(conn: aiosqlite.Connection) -> DemoServices:
     parental_leave = SQLiteParentalLeaveRepository(conn)
     planned_leave = SQLitePlannedLeaveRepository(conn)
 
-    analytics = AnalyticsService(parental_leave, planned_leave, children, personal_data, workspaces)
+    analytics = AnalyticsService(
+        parental_leave, planned_leave, children, personal_data, workspaces, vacation_repo
+    )
 
     return DemoServices(
         auth=AuthService(users, personal_data, workspaces),