FN-5912: separate planning summary button loading states

Keep planning summary actions responsive with operation-specific loading indicators.

- pass separate single-task and breakdown loading flags into the planning summary view
- show the Creating spinner only on Create Single Task and the Breaking down spinner only on Break into Tasks while keeping the sibling action disabled
- add regression coverage for both pending-action paths and normalize the restart integration test temp worktree root under /private/tmp

Files changed:
 .../dashboard/app/components/PlanningModeModal.tsx |  14 ++-
 .../PlanningModeModal.planning-flow.test.tsx       | 138 +++++++++++++++++++++
 .../src/__tests__/restart.integration.test.ts      |   7 +-
 3 files changed, 151 insertions(+), 8 deletions(-)

Fusion-Task-Id: FN-5912

Fusion-Task-Lineage: b93da566-0c2b-4ff8-83ea-b6e009dfd650

packages/engine/src/__tests__/restart.integration.test.ts

@@ -1298,7 +1298,8 @@ describe("Crash scenario edge cases", () => {
 
   it("concurrent resumeOrphaned() calls don't double-execute the same task", async () => {
     const store = createMockStore();
-    const worktreePath = "/tmp/test/.worktrees/swift-falcon";
+    const rootDir = "/private/tmp/test";
+    const worktreePath = `${rootDir}/.worktrees/swift-falcon`;
     const task = makeTask("FN-092", "in-progress", {
       worktree: worktreePath,
       branch: "fusion/fn-092",
@@ -1314,7 +1315,7 @@ describe("Crash scenario edge cases", () => {
       }
       if (String(cmd) === "git worktree list --porcelain") {
         return [
-          "worktree /tmp/test",
+          `worktree ${rootDir}`,
           "HEAD abc123",
           "branch refs/heads/main",
           "",
@@ -1335,7 +1336,7 @@ describe("Crash scenario edge cases", () => {
       },
     } as any);
 
-    const executor = new TaskExecutor(store, "/tmp/test");
+    const executor = new TaskExecutor(store, rootDir);
 
     // First call starts execution
     const first = executor.resumeOrphaned();