refactor: collapse single-implementation interfaces

Nine interfaces had exactly one implementation and no test double — they existed
only to be named twice in a DI registration: IFindingsStore, IFindingsStoreLocator,
IPrimeScheduleSignal, IRefineRunner, IWeekReportService, IMergeCoordinator,
IMissionControlPane, IOnlineLoginService, ITaskListFilter. Consumers now depend on
the concrete type; the DTO records that shared those files moved next to their
implementation. IInteractiveLaunchSpecService stays — it carries 54 lines of
contract documentation, which is not ceremony.

IMergeCoordinator in particular had a redundant null object: MergeCoordinator with
a null Handler already no-ops, and every test used the real class with Handler set.

Filtering/ collapses from 8 files to 1. ITaskListFilter and TaskListFilterBase were
a double abstraction over four predicates, with MatchesAsContext => false declared
in both. SmartFlagFilter also compiled its expression twice (its own _flag plus the
inherited Matches cache) — it now uses the cache.

StaticTokenAuthProvider was in src but production uses ZitadelAuthProvider; it is
a test double, so it moves to the test project. Its own test goes away with it.

src/ClaudeDo.Ui/Views/MissionControl/MissionControlView.axaml

@@ -75,7 +75,7 @@
                     SelectedItem="{Binding FocusedPane}"
                     IsVisible="{Binding IsFocusMode}">
           <TabControl.ItemTemplate>
-            <DataTemplate x:DataType="vmm:IMissionControlPane">
+            <DataTemplate x:DataType="vmm:ConPtyPaneViewModel">
               <TextBlock Text="{Binding DisplayTitle}" TextTrimming="CharacterEllipsis" MaxWidth="160" />
             </DataTemplate>
           </TabControl.ItemTemplate>