v2.5.7: Reservation overhaul, Day Detail Panel, i18n, paste support, auto dark mode

BREAKING: Reservations have been completely rebuilt. Existing place-level
reservations are no longer used. All reservations must be re-created via
the Bookings tab. Your trips, places, and other data are unaffected.

Reservation System (rebuilt from scratch):
- Reservations now link to specific day assignments instead of places
- Same place on different days can have independent reservations
- New assignment picker in booking modal (grouped by day, searchable)
- Removed day/place dropdowns from booking form
- Reservation badges in day plan sidebar with type-specific icons
- Reservation details in place inspector (only for selected assignment)
- Reservation summary in day detail panel

Day Detail Panel (new):
- Opens on day click in the sidebar
- Detailed weather: hourly forecast, precipitation, wind, sunrise/sunset
- Historical climate averages for dates beyond 16 days
- Accommodation management with check-in/check-out, confirmation number
- Hotel assignment across multiple days with day range picker
- Reservation overview for the day

Places:
- Places can now be assigned to the same day multiple times
- Start time + end time fields (replaces single time field)
- Map badges show multiple position numbers (e.g. "1 · 4")
- Route optimization fixed for duplicate places
- File attachments during place editing (not just creation)
- Cover image upload during trip creation (not just editing)
- Paste support (Ctrl+V) for images in trip, place, and file forms

Internationalization:
- 200+ hardcoded German strings translated to i18n (EN + DE)
- Server error messages in English
- Category seeds in English for new installations
- All planner, register, photo, packing components translated

UI/UX:
- Auto dark mode (follows system preference, configurable in settings)
- Navbar toggle switches light/dark (overrides auto)
- Sidebar minimize buttons z-index fixed
- Transport mode selector removed from day plan
- CustomSelect supports grouped headers (isHeader option)
- Optimistic updates for day notes (instant feedback)
- Booking cards redesigned with type-colored headers and structured details

Weather:
- Wind speed in mph when using Fahrenheit setting
- Weather description language matches app language

Admin:
- Weather info panel replaces OpenWeatherMap key input
- "Recommended" badge styling updated

client/src/components/Planner/PlacesSidebar.jsx

@@ -204,19 +204,17 @@ export default function PlacesSidebar({
             </div>
             <div style={{ flex: 1, overflowY: 'auto', padding: '8px 12px 16px' }}>
               {days.map((day, i) => {
-                const alreadyAssigned = (assignments[String(day.id)] || []).some(a => a.place?.id === dayPickerPlace.id)
                 return (
                   <button
                     key={day.id}
-                    disabled={alreadyAssigned}
                     onClick={() => { onAssignToDay(dayPickerPlace.id, day.id); setDayPickerPlace(null) }}
                     style={{
                       display: 'flex', alignItems: 'center', gap: 10, width: '100%',
-                      padding: '12px 14px', borderRadius: 12, border: 'none', cursor: alreadyAssigned ? 'default' : 'pointer',
+                      padding: '12px 14px', borderRadius: 12, border: 'none', cursor: 'pointer',
                       background: 'transparent', fontFamily: 'inherit', textAlign: 'left',
-                      opacity: alreadyAssigned ? 0.4 : 1, transition: 'background 0.1s',
+                      transition: 'background 0.1s',
                     }}
-                    onMouseEnter={e => { if (!alreadyAssigned) e.currentTarget.style.background = 'var(--bg-hover)' }}
+                    onMouseEnter={e => e.currentTarget.style.background = 'var(--bg-hover)'}
                     onMouseLeave={e => e.currentTarget.style.background = 'transparent'}
                   >
                     <div style={{
@@ -230,7 +228,7 @@ export default function PlacesSidebar({
                       </div>
                       {day.date && <div style={{ fontSize: 11, color: 'var(--text-faint)' }}>{new Date(day.date + 'T00:00:00').toLocaleDateString()}</div>}
                     </div>
-                    {alreadyAssigned && <span style={{ fontSize: 11, color: 'var(--text-faint)' }}>✓</span>}
+                    {(assignments[String(day.id)] || []).some(a => a.place?.id === dayPickerPlace.id) && <span style={{ fontSize: 11, color: 'var(--text-faint)' }}>✓</span>}
                   </button>
                 )
               })}