Added start_date field to goal creation/editing form:
1. New "Startdatum" input field before "Zieldatum"
- Defaults to today
- Hint: "Startwert wird automatisch aus historischen Daten ermittelt"
2. Display start_date in goals list
- Shows next to start_value: "85 kg (01.01.26)"
- Compact format for better readability
3. Updated formData state
- Added start_date with today as default
- API calls automatically include it
User can now:
- Set historical start date (e.g., 3 months ago)
- Backend auto-populates start_value from that date
- See exact start date and value for each goal
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>