fix(ui): validate PowerUse window, explain effort and Prime Claude in Settings

Three usability-audit findings in Settings:
- An unparseable PowerUse window (e.g. "9:0") used to save silently as null
  (= round the clock), the opposite of what the typo implied. Validate() now
  rejects an unparseable start/end unless blank; the worker-side read-time
  tolerance is unchanged.
- "Effort" column header gets a tooltip explaining it's the model's reasoning
  effort (cost/depth tradeoff).
- The "Prime Claude" tab gets a tooltip explaining scheduled Claude runs
  (Ping / Fill My Day / custom prompt).

New locale keys added to en+de. Updated the PowerUse round-trip test that
asserted the old silent-normalize behavior.

src/ClaudeDo.Ui/Views/Modals/SettingsModalView.axaml

@@ -190,7 +190,8 @@
                            Opacity="0.6" FontSize="12" TextWrapping="Wrap"/>
                 <Grid ColumnDefinitions="90,12,*,12,110" Margin="0,4,0,0">
                   <TextBlock Grid.Column="0" Classes="eyebrow" Text="{loc:Tr settings.general.model}"/>
-                  <TextBlock Grid.Column="2" Classes="eyebrow" Text="{loc:Tr settings.general.effort}"/>
+                  <TextBlock Grid.Column="2" Classes="eyebrow" Text="{loc:Tr settings.general.effort}"
+                             ToolTip.Tip="{loc:Tr settings.general.effortHint}"/>
                   <TextBlock Grid.Column="4" Classes="eyebrow" Text="{loc:Tr settings.general.maxTurns}"/>
                 </Grid>
                 <ItemsControl ItemsSource="{Binding General.ModelPresets}">
@@ -307,7 +308,8 @@
           </ScrollViewer>
         </TabItem>
 
-        <TabItem Header="{loc:Tr settings.sidebar.categoryPrime}">
+        <TabItem Header="{loc:Tr settings.sidebar.categoryPrime}"
+                 ToolTip.Tip="{loc:Tr settings.sidebar.categoryPrimeHint}">
           <ScrollViewer>
             <StackPanel Spacing="12" Margin="0,8,0,0">
               <Border IsVisible="{Binding !HasLinkedRepo}"