show the thing: screenshots, and a harness that makes them

Nobody installs a desktop widget they have not seen. Three shots go in the
README -- the Nativity Fast, where the week runs through three fasting
levels; ROCOR on 7 January, where the corner reads 25 December and makes the
old-calendar point in one glance; and Great Week, which uses nearly every
level there is.

shot.qml renders the real widget on a plain backdrop at a fixed position on
the overlay layer, so a screen grab of that rectangle is the widget and never
whatever was behind it. Typikon gains a forDate property, which is what lets
a screenshot show Great Week in September, and is worth having anyway for
looking ahead.

The header note now always carries the church date instead of repeating the
season the line below it already gives.

quickshell/services/Typikon.qml

@@ -17,6 +17,9 @@ Singleton {
     property string jurisdiction: ""
     // Today plus the next six, so the week ahead is visible at a glance.
     property int days: 7
+    // Empty means today. Set it to an ISO date to look at a different one --
+    // useful for seeing what Great Week will ask of you before it arrives.
+    property string forDate: ""
 
     property bool available: false
     property string error: ""
@@ -51,6 +54,8 @@ Singleton {
     // midnight and at no other moment.
     readonly property string _day: Qt.formatDateTime(clock.date, "yyyy-MM-dd")
     on_DayChanged: root.refresh()
+    onJurisdictionChanged: root.refresh()
+    onForDateChanged: root.refresh()
     Component.onCompleted: root.refresh()
 
     Process {
@@ -59,6 +64,8 @@ Singleton {
             const c = ["typikon", "--json", "--days", String(root.days)];
             if (root.jurisdiction !== "")
                 c.push("--jurisdiction", root.jurisdiction);
+            if (root.forDate !== "")
+                c.push("--date", root.forDate);
             return c;
         }
         stdout: StdioCollector {