feat(scheduling,admin,today): week-range queries, file size limits, mobile nav UX

- Expand exceptional application query to Monday of start week
- Add 20MB file size limit with visual feedback in ImageUpload
- Reorder admin nav links, add burger badge, slide transition + backdrop
- Fetch week-range working/available hours, add closing time indicator
- Skip lunch protection for days <= 5h via shouldApplyLunchProtection
- Extract formatDateISO to shared utils

backend/handlers/scheduling/default-hours.go

@@ -141,11 +141,19 @@ func GetWorkingHours(w http.ResponseWriter, r *http.Request) {
 	defRows.Close()
 
 	// Load exceptional applications for Mondays in range
+	// Expand start to the Monday of its week so single-day queries still find the correct application
+	startWeekday := int(start.Weekday())
+	daysSinceMonday := startWeekday - 1
+	if daysSinceMonday < 0 {
+		daysSinceMonday = 6 // Sunday
+	}
+	queryStart := start.AddDate(0, 0, -daysSinceMonday)
+
 	appRows, _ := db.DB.Query(r.Context(), `
 		SELECT group_id, week_start
 		FROM exceptional_group_applications
 		WHERE week_start BETWEEN $1 AND $2
-	`, start, end)
+	`, queryStart, end)
 	type appEntry struct {
 		GroupID   int
 		WeekStart time.Time
@@ -321,11 +329,19 @@ func GetAvailableHours(w http.ResponseWriter, r *http.Request) {
 	defRows.Close()
 
 	// Load exceptional applications for Mondays in range
+	// Expand start to the Monday of its week so single-day queries still find the correct application
+	startWeekday := int(start.Weekday())
+	daysSinceMonday := startWeekday - 1
+	if daysSinceMonday < 0 {
+		daysSinceMonday = 6 // Sunday
+	}
+	queryStart := start.AddDate(0, 0, -daysSinceMonday)
+
 	appRows, _ := db.DB.Query(r.Context(), `
 		SELECT group_id, week_start
 		FROM exceptional_group_applications
 		WHERE week_start BETWEEN $1 AND $2
-	`, start, end)
+	`, queryStart, end)
 	type appEntry struct {
 		GroupID   int
 		WeekStart time.Time