feat(dashboard): add selectable standup verification date and wire selected-date status
## Summary
Adds dynamic date selection for standup verification so users can check completion for any selected day (not only current date).
## What changed
- Added a calendar date input (`type="date"`) in `src/components/dashboard/DashboardLayout.tsx`.
- Wired team verification to use the selected date in `verifyStandupSubmission(...)`.
- Reset verification state when date changes to prevent stale results from another day.
- Updated UI labels from “Today ...” to selected-date-aware text in:
- `src/components/dashboard/TeamList.tsx`
- `src/components/intern/InternCard.tsx`
## Scope
Only these files were changed:
- `src/components/dashboard/DashboardLayout.tsx`
- `src/components/dashboard/TeamList.tsx`
- `src/components/intern/InternCard.tsx`
## Validation
- `npm run build` passed successfully.