Let a day removed from a period stay removed

Taking one day out of a period the planner placed did nothing that
lasted: the period still asked for a full week, so the next sync put the
day straight back. The option was disabled rather than lying about it.

A removed day is now recorded as its own thing — no leave for this
parent, this child, this date — and the planner honours it on every
later sync. It is kept apart from the working-day overrides, which
answer a different question about the calendar rather than about the
plan.

The day belongs to the parent whose band was clicked, so removing one
parent's day leaves their partner's alone; where both parents were to be
off on one funding arrangement, the partner is simply funded on their
own instead. A removed day shortens what the period is asking for rather
than counting as a day the plan failed to find, so the advice about
closing a shortfall does not start arguing for a day nobody wants.

Nothing is removed without a way back: the toast undoes it, and the day
itself is marked in the calendar and offers to restore.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ei7gCZzdd751uZtPzb1Pep

backend/app/main.py

@@ -28,6 +28,7 @@ from app.routers.fetch_data import router as fetch_data_router
 from app.routers.fetch_data import scraper_router
 from app.routers.leave_wishes import router as leave_wishes_router
 from app.routers.plan import router as plan_router
+from app.routers.planned_day_exclusions import router as planned_day_exclusions_router
 from app.routers.planned_days import router as planned_days_router
 from app.routers.settings import child_router, settings_child_router, tips_router
 from app.routers.workspace import _inv_router as invitations_router
@@ -126,6 +127,7 @@ def _register_routers(app: FastAPI) -> None:
     app.include_router(child_router)
     app.include_router(settings_child_router)
     app.include_router(planned_days_router)
+    app.include_router(planned_day_exclusions_router)
     app.include_router(vacation_days.router)
     app.include_router(day_overrides_router)
     app.include_router(calendar_router)