✨ feat: implement mock data support with API interceptor and update documentation

frontend/src/lib/api.ts

@@ -16,6 +16,7 @@ import { apiBaseOverride } from "./store"
 import { incrementRequests, decrementRequests } from "./requestsStore"
 import { setServerBuildTime } from "./serverBuildInfo"
 import { checkBuildVersion } from "./versionCheck"
+import { mockApiRequest } from "./mock"
 
 // ---------------------------------------------------------------------------
 // Request deduplication
@@ -84,6 +85,14 @@ export const api = async <T>(
             }
             incrementRequests()
 
+            // ── Mock interceptor (tree-shaken when __MOCK__ is false) ──
+            if (__MOCK__) {
+                const mockResult = mockApiRequest(endpoint, mergedOptions, body)
+                if (mockResult) return mockResult as ApiResult<T>
+                // No mock data for this endpoint → 404
+                throw { response: { status: 404 }, data: { error: `[mock] No mock data for "${endpoint}"` } }
+            }
+
             const data = await apiRequest(_apiBaseOverride + endpoint, mergedOptions, body, sentry)
 
             // Build-version check only on GETs (don't reload mid-write)