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/README.md

@@ -168,10 +168,10 @@ rewrites the `bar` subtree from the current `shell-defaults.json`.
   "bar": {
     "position": "top",
     "transparent": false,
-    "centerAnchor": "daytime",
+    "centerAnchor": "clock",
     "layout": {
       "left":   [ { "id": "omarchy" }, { "id": "workspaces" } ],
-      "center": [ { "id": "daytime", "format": "HH:mm" } ],
+      "center": [ { "id": "clock", "format": "HH:mm" } ],
       "right": [
         { "id": "audioPanel" }
       ]
@@ -194,8 +194,8 @@ rewrites the `bar` subtree from the current `shell-defaults.json`.
    settings UI adds/removes layout entries; other plugin kinds are enabled
    with the shell IPC. First-party plugins are always enabled.
 4. **Multiple instances** are allowed when a manifest sets
-   `allowMultiple: true`. Each instance is independent — e.g. two daytime
-   widgets in different timezones are just two `{"id":"daytime", "timezone": ...}`
+   `allowMultiple: true`. Each instance is independent — e.g. two clock
+   widgets in different timezones are just two `{"id":"clock", "timezone": ...}`
    entries with their own values.
 5. **Idle timings are top-level.** `idle.screensaver` and `idle.lock`
    are seconds since user idle began, so the default lock fires at 300s