fix(web): keep all-day drafts visible

[Uarmagan]

Summary

• Fix Day all-day draft creation so the same click that creates the draft does not immediately close the floating form.
• Make Day and Week use the same all-day draft placement helper, so a new draft lands after existing all-day events instead of covering the first row.
• Raise the event-form date picker above the floating event form.

Closes #1841

What was going wrong

• Day all-day creation could flash and disappear because the creating click was also being treated like an outside click after the draft/form opened.
• Week all-day drafts were rendered without being folded back through the all-day row assignment, so the draft could overlap the first saved all-day event.
• The date picker popover was lower than the floating form layer, so it appeared behind the draft form.

Main files

• packages/web/src/views/Day/components/Calendar/DayCalendarGrid.tsx
• packages/web/src/views/Day/components/Calendar/dayCalendarDraft.util.ts
• packages/web/src/common/calendar-grid/layout/allDayDraftEventPosition.ts
• packages/web/src/views/Week/components/Draft/Draft.tsx
• packages/web/src/views/Week/components/Draft/grid/GridDraft.tsx
• packages/web/src/components/DatePicker/DatePicker.tsx

Validation

• Browser: Day top-band all-day click opens the draft and the form stays open at http://localhost:9080/day/2026-05-31
• Browser: event-form date picker renders above the floating form (datepicker z-index 22, form z-index 21)
• bun run test:web
• bun test --cwd packages/web src/components/PlannerSidebar/SomedayEventSections/SomedayEventSections.test.tsx
• bun test --cwd packages/web src/common/calendar-grid/layout/allDayDraftEventPosition.test.ts src/views/Day/components/Calendar/DayCalendarGrid.test.tsx src/views/Week/components/Draft/grid/GridDraft.test.tsx
• bun lint
• bun run type-check
• bun run build:web
• git diff --check
• react-doctor --diff: 100/100, with one pre-existing DatePicker customInput warning left unchanged

CI

• GitHub checks are green on the rebased branch: e2e, web unit, type-check, backend/core/scripts unit tests, and CodeQL.