refactor(api): streamline API requests with requestJson and requestBlob functions

Replaced direct fetch calls with requestJson and requestBlob utility functions across multiple components for improved consistency and error handling. This change enhances the maintainability of the codebase by centralizing API request logic and ensuring uniform handling of authentication and response parsing.

lib/data-source.tsx

@@ -9,6 +9,7 @@ import {
   LOCAL_DEFAULT_BACKEND_URL,
   resolveStoredBackendUrl,
 } from "@/lib/backend-url"
+import { resolveApiUrl } from "@/shared/api/http-client"
 
 // ── types ─────────────────────────────────────────────────────────────────────
 
@@ -49,8 +50,13 @@ function readStoredMode(): DataSourceMode {
   return defaultDataSourceMode()
 }
 
-function readStoredBackendUrl(): string {
-  if (typeof window === "undefined") return LOCAL_DEFAULT_BACKEND_URL
+function initialBackendUrl(): string {
+  if (typeof window === "undefined") {
+    const cfg = configuredBackendUrl()
+    if (cfg.kind === "same-origin") return ""
+    if (cfg.kind === "fixed") return cfg.url
+    return LOCAL_DEFAULT_BACKEND_URL
+  }
   return resolveStoredBackendUrl(localStorage.getItem(LS_BACKEND))
 }
 
@@ -60,7 +66,7 @@ function normalizeBackendUrl(url: string): string {
 
 export function DataSourceProvider({ children }: { children: React.ReactNode }) {
   const [mode, setModeState] = useState<DataSourceMode>(defaultDataSourceMode)
-  const [backendUrl, setBackendUrlState] = useState(LOCAL_DEFAULT_BACKEND_URL)
+  const [backendUrl, setBackendUrlState] = useState(initialBackendUrl)
   const [prefsHydrated, setPrefsHydrated] = useState(false)
   const [backendStatus, setBackendStatus] = useState<boolean | undefined>(undefined)
   const backendUrlLocked = isBackendUrlLocked()
@@ -68,10 +74,7 @@ export function DataSourceProvider({ children }: { children: React.ReactNode })
 
   useEffect(() => {
     const storedMode = readStoredMode()
-    let url = readStoredBackendUrl()
-    if (configuredBackendUrl().kind === "same-origin") {
-      url = window.location.origin
-    }
+    const url = resolveStoredBackendUrl(localStorage.getItem(LS_BACKEND))
     setModeState(storedMode)
     setBackendUrlState(url)
     setPrefsHydrated(true)
@@ -91,10 +94,7 @@ export function DataSourceProvider({ children }: { children: React.ReactNode })
   }, [backendUrlLocked])
 
   const checkBackend = useCallback(async () => {
-    const healthUrl =
-      configuredBackendUrl().kind === "same-origin"
-        ? "/health"
-        : `${normalizeBackendUrl(backendUrl)}/health`
+    const healthUrl = resolveApiUrl(backendUrl, "/health")
     try {
       const res = await fetch(healthUrl, { signal: AbortSignal.timeout(3000) })
       setBackendStatus(res.ok)