Drop the daytime widget, use clock everywhere

Clock and daytime were near-duplicates with different click semantics
(clock toggles between formats on left-click and opens the timezone
selector on right-click; daytime was non-pressable with a hover tooltip).
Standardize on clock, since it's the more capable of the two.

- Delete widgets/daytime.qml and its FirstPartyWidgets entry.
- Migrate shell-defaults.json, shell.qml's builtin fallback, Bar.qml's
  fallback bar config, and the settings panel's builtin defaults so the
  center anchor and center-section entry both reference "clock".
- Rename the daytimeSettings form to clockSettings and rephrase
  "Tooltip format" → "Alternate format (click to toggle)" so the field
  label matches clock's actual behavior.
- Update the gallery dropdown options and bar/README docs.

shell/shell.qml

@@ -44,10 +44,10 @@ ShellRoot {
     bar: {
       position: "top",
       transparent: false,
-      centerAnchor: "daytime",
+      centerAnchor: "clock",
       layout: {
         left: [{ id: "omarchy" }, { id: "workspaces" }],
-        center: [{ id: "daytime", format: "dddd HH:mm" }],
+        center: [{ id: "clock", format: "dddd HH:mm" }],
         right: [{ id: "audioPanel" }]
       }
     },
@@ -491,7 +491,7 @@ ShellRoot {
   // Mirror plugin registry state into BarWidgetRegistry whenever it changes.
   // Each enabled plugin with kind "bar-widget" gets a Component created from
   // its manifest entry point and registered under its plain manifest id.
-  // First-party widget ids (daytime, weather, etc.) are short and don't
+  // First-party widget ids (clock, weather, etc.) are short and don't
   // collide with namespaced plugin ids, so we don't need a separate
   // "plugin:" namespace anymore.
   Connections {