Let the planner fund a hand-drawn period, and remove one at a time

Three changes to calendar editing, too interleaved in the same files to
land separately.

Giving the same days to the second parent rewrote the first parent's
days instead of adding their own. The save looked the existing day up
against whoever was logged in rather than the parent being saved for, so
parent A's leave turned into parent B's vacation. The parent choice now
lives with the lookup, and two parents on the same dates produce two
rows and two bands.

Drawing a period by hand meant naming a day type up front. It now asks
who is off and lets the planner fund it, as a one-off period the sync
places, with double days offered when both parents are off and priced
honestly in the hint. Pinning an exact day type is still there, moved
behind Advanced, and editing a pinned day goes straight back to it.

Removing a period offered only the two extremes. There are now three
choices: this day, this year's period, or every year. Taking one year
out of a repeating period narrows it, or splits it in two when the year
is in the middle; where a scope cannot be expressed it is disabled with
a reason rather than doing something surprising.

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

frontend/tests/fixtures/mockData.ts

@@ -148,6 +148,7 @@ export function makeLeaveWish(overrides: Partial<LeaveWish> = {}): LeaveWish {
     parentMode: 'either',
     parentPersonalDataUuid: null,
     windowMode: 'fixed',
+    wantsDubbeldag: false,
     createdAt: '2026-01-01T00:00:00',
     updatedAt: '2026-01-01T00:00:00',
     ...overrides,