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/shared/CustomSelect.jsx

@@ -51,7 +51,7 @@ export default function CustomSelect({
           background: 'var(--bg-input)', color: 'var(--text-primary)',
           fontSize: 13, fontWeight: 500, fontFamily: 'inherit',
           cursor: 'pointer', outline: 'none', textAlign: 'left',
-          transition: 'border-color 0.15s',
+          transition: 'border-color 0.15s', overflow: 'hidden', minWidth: 0,
         }}
         onMouseEnter={e => e.currentTarget.style.borderColor = 'var(--text-faint)'}
         onMouseLeave={e => { if (!open) e.currentTarget.style.borderColor = 'var(--border-primary)' }}
@@ -105,6 +105,17 @@ export default function CustomSelect({
               <div style={{ padding: '10px 12px', fontSize: 12, color: 'var(--text-faint)', textAlign: 'center' }}>—</div>
             ) : (
               filtered.map(option => {
+                if (option.isHeader) {
+                  return (
+                    <div key={option.value} style={{
+                      padding: '5px 10px', fontSize: 10, fontWeight: 700, color: 'var(--text-faint)',
+                      textTransform: 'uppercase', letterSpacing: '0.03em',
+                      background: 'var(--bg-tertiary)', borderRadius: 4, margin: '2px 0',
+                    }}>
+                      {option.label}
+                    </div>
+                  )
+                }
                 const isSelected = option.value === value
                 return (
                   <button