Add calendar color support (DAVx5 calendar-color)

Calendars can now have a color (hex, e.g. #3b82f6) that DAVx5 and other
CalDAV clients pick up via the Apple/dav4jvm calendar-color property.

- db: add calendars.color column with migration for existing DBs;
  CreateCalendarWithColor, SetCalendarColor, GetCalendarColor;
  ListCalendars now returns []Calendar{Name, Color} instead of []string
- caldav: since go-webdav's caldav.Backend interface has no extension
  point for vendor properties, wrap the handler with a response-rewriting
  middleware that injects <calendar-color xmlns="http://apple.com/ns/ical/">
  into PROPFIND responses for calendars that have a color set
- web: color picker on the "New calendar" form and an inline color swatch/
  picker on each calendar card (calendars only, not address books)
- nidusctl: `calendar create --color` flag and a new `calendar color`
  subcommand; `calendar list` now also prints the color if set

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tools/nidusctl/main.go

@@ -80,7 +80,8 @@ Usage:
   nidusctl [-config config.yaml] user list
   nidusctl [-config config.yaml] user passwd   <username> [--password PW]
 
-  nidusctl [-config config.yaml] calendar create   <owner> <calendar>
+  nidusctl [-config config.yaml] calendar create   <owner> <calendar> [--color '#RRGGBB']
+  nidusctl [-config config.yaml] calendar color    <owner> <calendar> <hex-color>
   nidusctl [-config config.yaml] calendar delete   <owner> <calendar>
   nidusctl [-config config.yaml] calendar list     <owner>
   nidusctl [-config config.yaml] calendar share    <owner> <calendar> <user> <read|write>
@@ -117,12 +118,17 @@ func runCalendar(dbase *db.DB, st *store.Store, args []string) int {
 	}
 	switch args[0] {
 	case "create":
-		if len(args) != 3 {
-			fmt.Fprintln(os.Stderr, "usage: nidusctl calendar create <owner> <calendar>")
+		fs := newFlagSet("calendar create")
+		color := fs.String("color", "", "hex color like #3b82f6 (optional)")
+		if err := fs.Parse(args[1:]); err != nil {
 			return 2
 		}
-		owner, calName := args[1], args[2]
-		if err := dbase.CreateCalendar(owner, calName); err != nil {
+		if fs.NArg() != 2 {
+			fmt.Fprintln(os.Stderr, "usage: nidusctl calendar create <owner> <calendar> [--color '#RRGGBB']")
+			return 2
+		}
+		owner, calName := fs.Arg(0), fs.Arg(1)
+		if err := dbase.CreateCalendarWithColor(owner, calName, *color); err != nil {
 			fmt.Fprintf(os.Stderr, "error: %v\n", err)
 			return 1
 		}
@@ -132,6 +138,19 @@ func runCalendar(dbase *db.DB, st *store.Store, args []string) int {
 		fmt.Printf("created calendar %q for %s\n", calName, owner)
 		return 0
 
+	case "color":
+		if len(args) != 4 {
+			fmt.Fprintln(os.Stderr, "usage: nidusctl calendar color <owner> <calendar> <hex-color>")
+			return 2
+		}
+		owner, calName, color := args[1], args[2], args[3]
+		if err := dbase.SetCalendarColor(owner, calName, color); err != nil {
+			fmt.Fprintf(os.Stderr, "error: %v\n", err)
+			return 1
+		}
+		fmt.Printf("set color of calendar %q for %s to %s\n", calName, owner, color)
+		return 0
+
 	case "delete":
 		if len(args) != 3 {
 			fmt.Fprintln(os.Stderr, "usage: nidusctl calendar delete <owner> <calendar>")
@@ -154,13 +173,17 @@ func runCalendar(dbase *db.DB, st *store.Store, args []string) int {
 			return 2
 		}
 		owner := args[1]
-		names, err := dbase.ListCalendars(owner)
+		cals, err := dbase.ListCalendars(owner)
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "error: %v\n", err)
 			return 1
 		}
-		for _, n := range names {
-			fmt.Println(n)
+		for _, c := range cals {
+			if c.Color != "" {
+				fmt.Printf("%s\t%s\n", c.Name, c.Color)
+			} else {
+				fmt.Println(c.Name)
+			}
 		}
 		return 0