feat: add case reorder and delete in Manage tab

Add a "Manage" tab to the create-case modal with up/down reorder
buttons and delete for each case. Linked cases are unlinked (folder
preserved); CASES_DIR cases are permanently deleted.

Backend:
- DELETE /api/cases/:name — unlink or delete
- PUT /api/cases/order — persist ordering to settings.json
- GET /api/cases now respects saved caseOrder

Frontend:
- Third "Manage" tab in createCaseModal with case list
- Delete button in mobile case picker bottom sheet
- SSE events: case:deleted, case:order-changed

src/web/schemas.ts

@@ -431,6 +431,11 @@ export const LinkCaseSchema = z.object({
   path: safePathSchema,
 });
 
+/** PUT /api/cases/order */
+export const CaseOrderSchema = z.object({
+  order: z.array(z.string().regex(/^[a-zA-Z0-9_-]+$/, 'Invalid case name format')),
+});
+
 /** POST /api/auth/revoke */
 export const RevokeSessionSchema = z.object({
   sessionToken: z.string().min(1).max(200).optional(),