feat(notes): notes get their own list, a day log and an Enter chain

The editor was reachable from one button that only appeared in My Day,
which is how it got forgotten. It is now a permanent sidebar entry next
to My Day and Planned, and it fills the tasks island rather than the
details pane, because a note list is content.

Inside, the date picker is gone: today sits at the top with the capture
box, older days follow as dated groups. Enter in a note saves it and
opens the next one, Shift+Enter breaks the line so notes can be several,
Backspace on an empty note deletes it and steps back up. Deleting also
has a visible hover button instead of only "clear the text and hope".
Agent-written notes carry a marker.

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

src/ClaudeDo.Ui/Views/Islands/DetailsIslandView.axaml

@@ -125,17 +125,12 @@
                       DragCompleted="OnSplitterDragCompleted"/>
       </Grid>
 
-      <!-- Empty state: no task selected, outside Notes/Prep mode -->
+      <!-- Empty state: no task selected, outside Prep mode -->
       <TextBlock IsVisible="{Binding IsEmptyStateVisible}"
                  Text="{loc:Tr details.emptyState}"
                  Foreground="{DynamicResource TextMuteBrush}"
                  HorizontalAlignment="Center" VerticalAlignment="Center"/>
 
-      <!-- Notes mode -->
-      <Panel IsVisible="{Binding IsNotesMode}">
-        <islands:NotesEditorView DataContext="{Binding Notes}"/>
-      </Panel>
-
       <!-- Daily-prep mode -->
       <Panel IsVisible="{Binding IsPrepMode}">
         <DockPanel>