feat(03-02): add SocialDraftPreview component and ApprovalInspector integration

- Create SocialDraftPreview with platform icon, color, content, char count, media URLs, schedule display
- Integrate SocialDraftPreview into ApprovalInspector for social_post approvals
- Add schedule picker with immediate/scheduled radio group and datetime-local input
- Add social_post to type badge with accent styling
- Approve button shows 'Approve & Post' for social_post approvals
- Accessibility: role=region, aria-label, aria-live=polite, role=radiogroup
- Fix test type annotation for TS compatibility

tests/unit/social-draft.test.ts

@@ -175,7 +175,7 @@ describe("social draft pipeline", () => {
     it("rejected social_post creates no browser action", () => {
       // When decision is "rejected", the social_post handler should NOT run saveBrowserAction.
       // This validates the condition: approval.type === "social_post" && decision === "approved"
-      const decision = "rejected";
+      const decision: string = "rejected";
       const shouldCreateAction = decision === "approved";
       expect(shouldCreateAction).toBe(false);
     });