test(FN-2197): reconcile skipped-test inventory and stabilize planning resume coverage

- Add docs/skipped-test-inventory.md with the current intentional skip patterns and rationale across test suites
- Link the skipped-test inventory from docs/README.md for easier discovery
- Record reconciliation of older skip follow-up tasks that are now covered and no longer active backlog
- Stabilize PlanningModeModal conversation-history resume testing by overriding stream behavior in the targeted test case

packages/dashboard/app/components/PlanningModeModal.test.tsx

@@ -884,6 +884,11 @@ describe("PlanningModeModal", () => {
 
   describe("Conversation history", () => {
     it("restores all persisted Q&A pairs when resuming a session", async () => {
+      mockConnectPlanningStream.mockImplementationOnce(() => ({
+        close: vi.fn(),
+        isConnected: vi.fn().mockReturnValue(true),
+      }));
+
       const resumedQuestion: PlanningQuestion = {
         id: "q-current",
         type: "text",