feat(11-01): schema, service, and tests for sort_order + reorderCandidates

- Add sortOrder REAL column to threadCandidates schema (default 0)
- Add sort_order column to test helper CREATE TABLE
- Add reorderCandidatesSchema to shared/schemas.ts
- Add ReorderCandidates type to shared/types.ts
- getThreadWithCandidates now orders candidates by sort_order ASC
- createCandidate appends at max sort_order + 1000 (first = 1000)
- Add reorderCandidates service function (transaction, active-only guard)
- Add 5 new tests: ordering, appending, reorder success, resolved guard, missing thread

src/shared/schemas.ts

@@ -63,6 +63,10 @@ export const resolveThreadSchema = z.object({
 	candidateId: z.number().int().positive(),
 });
 
+export const reorderCandidatesSchema = z.object({
+	orderedIds: z.array(z.number().int().positive()).min(1),
+});
+
 // Setup schemas
 export const createSetupSchema = z.object({
 	name: z.string().min(1, "Setup name is required"),