feat(web): board and calendar views, saved filters and label pages

The board is one column per section with native drag-and-drop, which
works with a trackpad, a mouse and a screen reader without any of them
being reimplemented. Dropping is optimistic: a card that snaps back for
200ms reads as a failed drop.

Weeks in the calendar start on Monday. That is ISO 8601 and what every
Danish calendar does; a Sunday-first grid makes a Dane misread the month
at a glance. On a phone the chips give way to coloured bars — at that
width the month's shape is the useful part, not the titles.

Label pages run the filter language rather than a bespoke endpoint, so a
label page and a saved filter can never disagree about what a label
selects.

fix(recurrence): "hver mandag", not "hver uge mandag"

A weekly rule that names its days does not also need the word for the
interval. That is how the phrase is said, and it is what the parser
accepts back — the round trip through Describe now holds for weekday
rules too.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/recurrence/recurrence.go

@@ -298,7 +298,15 @@ func Describe(rule string) string {
 		for _, code := range strings.Split(days, ",") {
 			names = append(names, danishDay(code))
 		}
-		return every(interval, "uge") + " " + strings.Join(names, " og ")
+		joined := strings.Join(names, " og ")
+
+		// "hver mandag", not "hver uge mandag". A weekly rule naming its days does
+		// not also need the word for the interval — that is how the phrase is said,
+		// and it is what the parser accepts back.
+		if interval <= 1 {
+			return "hver " + joined
+		}
+		return every(interval, "uge") + " " + joined
 	}
 
 	switch parts["FREQ"] {