Let vacation years go back to the child's birth year

Settings only offered vacation-day rows from the current year forward,
while analytics ran its balance series from the child's birth year. Every
year in the gap had no vacation_days row, so the series assumed a full
statutory 25 earned with no use and banked earned - floor of it forward —
phantom saved days the user had no row to correct.

Settings now offers editable rows back to the birth year, and a past year
with no row assumes only the floor was earned, so it banks nothing. A past
year the user did enter is untouched by that rule.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/app/services/tips_service.py

@@ -785,8 +785,18 @@ class TipsService:
             known_years = {v.year for v in rows} | set(use_by_year.keys()) | {today.year}
             start_year = min(min(known_years), today.year - (carry_years - 1))
             years = list(range(start_year, today.year + 1))
+            # `years` reaches back to `today.year - (carry_years - 1)` (or an
+            # earlier known year) so the FIFO bank simulation can correctly
+            # age out old entries by `today.year` — those earlier years are
+            # real past years, not a forecast, so they get the same
+            # past-year `earned = floor` assumption as Settings/Analytics
+            # for a year with no row (`current_year=today.year`), rather
+            # than silently assuming the full statutory default the way a
+            # future year would. Keeps this tip's forfeiture warning from
+            # disagreeing with the dashboard's own numbers for the same
+            # unconfirmed past year.
             series = AnalyticsService._vacation_year_series(
-                years, vacation_by_year, use_by_year, pd.min_vacation_days_per_year
+                years, vacation_by_year, use_by_year, pd.min_vacation_days_per_year, today.year
             )
             vacation_year_balance_by_parent[pd.uuid] = series[-1]