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

frontend/tests/fixtures/hooks.ts

@@ -18,6 +18,7 @@ import type { usePlannedDays } from '@/hooks/usePlannedDays'
 import type { useScraperFetch } from '@/hooks/useScraperFetch'
 import type { useWorkspaceMembers } from '@/hooks/useWorkspaceMembers'
 import type { useOptimizationTips } from '@/hooks/useOptimizationTips'
+import type { usePlannedDayExclusions } from '@/hooks/usePlannedDayExclusions'
 import type { useDayOverrides } from '@/hooks/useDayOverrides'
 import type { useLeaveWishes } from '@/hooks/useLeaveWishes'
 import type { usePlanProposal } from '@/hooks/usePlanProposal'
@@ -172,6 +173,19 @@ export function makeDayOverridesResult(
   }
 }
 
+export function makePlannedDayExclusionsResult(
+  overrides: Partial<ReturnType<typeof usePlannedDayExclusions>> = {},
+): ReturnType<typeof usePlannedDayExclusions> {
+  return {
+    data: [],
+    isLoading: false,
+    error: null,
+    exclude: vi.fn(),
+    restore: vi.fn(),
+    ...overrides,
+  }
+}
+
 export function makeLeaveWishesResult(
   overrides: Partial<ReturnType<typeof useLeaveWishes>> = {},
 ): ReturnType<typeof useLeaveWishes> {