feat(10-01): wire pros/cons through client hooks, form, and card indicator

- CandidateResponse: add pros/cons string|null fields
- CandidateForm: add pros/cons to FormData, INITIAL_FORM, pre-fill, payload
- CandidateForm: add Pros/Cons textarea inputs (after Notes, before Product Link)
- CandidateCard: add pros/cons props, render purple +/- Notes badge when present
- Thread detail route: pass pros/cons props to CandidateCard

src/client/hooks/useCandidates.ts

@@ -13,6 +13,8 @@ interface CandidateResponse {
 	productUrl: string | null;
 	imageFilename: string | null;
 	status: "researching" | "ordered" | "arrived";
+	pros: string | null;
+	cons: string | null;
 	createdAt: string;
 	updatedAt: string;
 }