build: complete Phase 2.1B backend sync integration

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

__tests__/lib/cache-manager.test.ts

@@ -71,6 +71,43 @@ const mockIndexedDB = (() => {
                     setTimeout(() => req.onsuccess?.(), 0)
                     return req
                   },
+                  openCursor: () => {
+                    const keys = Object.keys(stores[name])
+                    let index = 0
+                    const req: any = {
+                      result: null,
+                      onsuccess: null
+                    }
+                    setTimeout(() => {
+                      if (index < keys.length) {
+                        req.result = {
+                          value: stores[name][keys[index]],
+                          delete: () => {
+                            delete stores[name][keys[index]]
+                          },
+                          continue: () => {
+                            index++
+                            setTimeout(() => {
+                              if (index < keys.length) {
+                                req.result = {
+                                  value: stores[name][keys[index]],
+                                  delete: () => {
+                                    delete stores[name][keys[index]]
+                                  },
+                                  continue: req.result.continue
+                                }
+                              } else {
+                                req.result = null
+                              }
+                              req.onsuccess?.({ target: req })
+                            }, 0)
+                          }
+                        }
+                      }
+                      req.onsuccess?.({ target: req })
+                    }, 0)
+                    return req
+                  },
                   index: (indexName: string) => {
                     return {
                       openCursor: (range?: any) => {