A week that starts where the person reading it starts theirs

The scheduler's day picker began on Sunday because that is where Intl
numbers the days from, which is a fact about the API and not about
anybody's week. Monday leads it across most of Europe. A row of seven
buttons in the wrong order is not just odd to read — it is easy to
misclick, and a misclicked day in a schedule is a car charging on the
wrong night.

So Settings › Appearance asks, beneath the date and the clock, as the
third question a region gets: first day of the week, following the region
unless it is answered outright. The same shape the time format already
had, and the same "auto" default, so nothing changes for an account that
never opens it.

The rule lives in lib/format.js beside the clock's, with the ordering, the
day names and the sort all coming from there. The two places that lay
weekdays out — the picker and the line each task is summarised on — read
it rather than each keeping an opinion, so a day set is written and read
back in the same order.

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

API Server/internal/api/me.go

@@ -30,6 +30,7 @@ type userRecord struct {
 	Locale              string `json:"locale"`
 	DateFormat          string `json:"date_format"`
 	TimeFormat          string `json:"time_format"`
+	WeekStart           string `json:"week_start"`
 	Currency            string `json:"currency"`
 	FontSize            string `json:"font_size"`
 	DragLocked          bool   `json:"drag_locked"`
@@ -99,6 +100,7 @@ func (rec userRecord) toModel() models.User {
 		Locale:     orDefault(rec.Locale, "en-US"),
 		DateFormat: orDefault(rec.DateFormat, "YMD"),
 		TimeFormat: orDefault(rec.TimeFormat, "auto"),
+		WeekStart:  orDefault(rec.WeekStart, "auto"),
 		Currency:   orDefault(rec.Currency, "USD"),
 		FontSize:   orDefault(rec.FontSize, "medium"),
 		DragLocked: rec.DragLocked,
@@ -164,6 +166,7 @@ type updateMeRequest struct {
 	Locale           *string   `json:"locale"`
 	DateFormat       *string   `json:"dateFormat"`
 	TimeFormat       *string   `json:"timeFormat"`
+	WeekStart        *string   `json:"weekStart"`
 	Currency         *string   `json:"currency"`
 	FontSize         *string   `json:"fontSize"`
 	DragLocked       *bool     `json:"dragLocked"`
@@ -264,6 +267,12 @@ var validDateFormats = map[string]bool{"YMD": true, "DMY_NUM": true, "DMY": true
 // the app did before there was a setting; the other two say it outright, for
 // the people whose region and habit disagree.
 var validTimeFormats = map[string]bool{"auto": true, "24": true, "12": true}
+
+// Which day a week is drawn as starting on. "auto" is the chosen region's own
+// convention — Monday across most of Europe, Sunday in the US — and is what
+// every weekday row read before there was a setting; the other two say it
+// outright, for the people whose region and habit disagree.
+var validWeekStarts = map[string]bool{"auto": true, "monday": true, "sunday": true}
 var validFontSizes = map[string]bool{"small": true, "medium": true, "large": true}
 
 // Kept in step with the users.currency select options in setup-pocketbase.mjs:
@@ -333,6 +342,13 @@ func (s *Server) handleUpdateMe(w http.ResponseWriter, r *http.Request) {
 		}
 		payload["time_format"] = *in.TimeFormat
 	}
+	if in.WeekStart != nil {
+		if !validWeekStarts[*in.WeekStart] {
+			writeError(w, http.StatusBadRequest, "weekStart must be auto, monday, or sunday")
+			return
+		}
+		payload["week_start"] = *in.WeekStart
+	}
 	if in.Currency != nil {
 		if !validCurrencies[*in.Currency] {
 			writeError(w, http.StatusBadRequest, "currency must be a supported ISO 4217 code")