feat(ui): richer diff viewer + surface child roadblocks on parents

- UnifiedDiffParser detects added/deleted/renamed/binary files; diff
  modal shows a file list, binary/empty placeholders, and can diff a
  merged task by commit range after its worktree is gone
- DetailsIslandViewModel flags children needing attention (failed,
  cancelled, awaiting review, or with roadblocks) on the parent
- GitService gains worktree head-commit/range support; planning chain,
  merge orchestration, and session manager tweaks with updated tests
- refresh app/installer/worker icons

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs

@@ -19,17 +19,21 @@ public sealed class PlanningChainCoordinator
         _state = state;
     }
 
-    // Sets up a sequential queue chain over a planning parent's children.
-    // - First non-terminal child gets Status=Queued, BlockedByTaskId=null.
-    // - Each subsequent non-terminal child gets Status=Queued + BlockedByTaskId=<predecessor>,
+    // Sets up a sequential chain over a planning parent's children.
+    // - First non-terminal child gets BlockedByTaskId=null.
+    // - Each subsequent non-terminal child gets BlockedByTaskId=<predecessor>,
     //   so the picker skips them until the predecessor finishes.
+    // - When enqueue is true, each non-terminal child is also set to Status=Queued
+    //   (the user-driven "Queue plan"). When false (finalize), children are left
+    //   Idle and only the blocked-by links are established, so nothing runs until
+    //   the user queues the plan.
     // - Terminal children (Done/Failed/Cancelled) are left untouched; they are
     //   skipped when computing predecessors so a re-run on a partially executed
     //   chain leaves history alone but still reshapes the tail.
     // - Running children abort the operation — the chain cannot be reshaped while
     //   one of its members is mid-flight.
     // Returns the number of children placed in the chain.
-    internal async Task<int> SetupChainAsync(string parentTaskId, CancellationToken ct = default)
+    internal async Task<int> SetupChainAsync(string parentTaskId, bool enqueue, CancellationToken ct = default)
     {
         await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
         var parent = await ctx.Tasks.FirstOrDefaultAsync(t => t.Id == parentTaskId, ct)
@@ -56,7 +60,8 @@ public sealed class PlanningChainCoordinator
         var state = _state();
         for (int i = 0; i < sequenceable.Count; i++)
         {
-            await state.EnqueueAsync(sequenceable[i].Id, ct);
+            if (enqueue)
+                await state.EnqueueAsync(sequenceable[i].Id, ct);
             if (i == 0)
                 await state.UnblockAsync(sequenceable[i].Id, ct);
             else
@@ -81,7 +86,7 @@ public sealed class PlanningChainCoordinator
         if (phase != PlanningPhase.Finalized)
             throw new InvalidOperationException("Plan must be finalized before it can be queued.");
 
-        return await SetupChainAsync(parentTaskId, ct);
+        return await SetupChainAsync(parentTaskId, enqueue: true, ct);
     }
 
     public async Task<string?> OnChildFinishedAsync(