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/CLAUDE.md

@@ -102,8 +102,10 @@ approve is the single review+merge action. Review transitions live in `TaskState
 `PlanningSessionManager.FinalizeAsync` is the single path:
 
 1. `_state.FinalizePlanningAsync(parent)` flips parent `PlanningPhase` to `Finalized` and sets `Status` to `WaitingForChildren` (or `WaitingForReview` if the parent has no children).
-2. `PlanningChainCoordinator.SetupChainAsync` attaches the `agent` tag to every child, enqueues child[0], and `BlockOn`s child[i] → child[i-1].
-3. The first child is woken automatically; successors unblock as their predecessor reaches a terminal state via `OnChildFinishedAsync`.
+2. `PlanningChainCoordinator.SetupChainAsync(parent, enqueue: false)` establishes the blocked-by chain (`BlockOn`s child[i] → child[i-1]) but **leaves children `Idle`** — finalize never auto-queues. Queueing is a deliberate user action: `QueuePlanAsync` (hub `QueuePlanningSubtasksAsync`, the "Queue plan" button) calls `SetupChainAsync(parent, enqueue: true)`, which sets every non-terminal child `Queued` and re-applies the chain.
+3. Once queued, the first child is woken automatically; successors unblock as their predecessor reaches a terminal state via `OnChildFinishedAsync`.
+
+A child that hits a roadblock (fails, or reports `CLAUDEDO_BLOCKED` roadblocks) does **not** advance the parent — the parent stays in `WaitingForChildren` until every child is terminal. The UI surfaces blocked children on the parent's Session tab (`ChildOutcomes` + a "children need attention" band) so the roadblock is visible without forcing a transition.
 
 `TaskRepository.FinalizePlanningAsync` no longer exists. The `Mark*Async` repository helpers are `internal` — only `TaskStateService` calls them.