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/sse-events.ts

@@ -325,6 +325,10 @@ export const OrchestratorError = 'orchestrator:error' as const;
 export const CaseCreated = 'case:created' as const;
 /** Existing directory linked as a case. */
 export const CaseLinked = 'case:linked' as const;
+/** Case deleted or unlinked. */
+export const CaseDeleted = 'case:deleted' as const;
+/** Case ordering changed. */
+export const CaseOrderChanged = 'case:order-changed' as const;
 
 // ─── Namespace Re-export ─────────────────────────────────────────────────────
 
@@ -485,4 +489,6 @@ export const SseEvent = {
   // Cases
   CaseCreated,
   CaseLinked,
+  CaseDeleted,
+  CaseOrderChanged,
 } as const;