Extract vendor page subcomponents; structured Directus errors

Split the 316-line vendors index into VendorToolbar, VendorGrid,
VendorList, and PerPageSelector under components/vendors/. Page now
owns only search-param state and query orchestration.

Replace generic Error throws in lib/directus.ts with a DirectusError
class carrying status, statusText, collection, url, and parsed body.
Surface useLocalStorage read/write failures via console.warn instead
of swallowing them.

frontend/src/hooks/use-local-storage.ts

@@ -6,7 +6,8 @@ export function useLocalStorage<T>(key: string, initialValue: T): [T, (v: T) =>
     try {
       const raw = window.localStorage.getItem(key)
       return raw != null ? (JSON.parse(raw) as T) : initialValue
-    } catch {
+    } catch (err) {
+      console.warn(`useLocalStorage: failed to read "${key}"`, err)
       return initialValue
     }
   })
@@ -14,8 +15,8 @@ export function useLocalStorage<T>(key: string, initialValue: T): [T, (v: T) =>
   useEffect(() => {
     try {
       window.localStorage.setItem(key, JSON.stringify(value))
-    } catch {
-      /* storage unavailable */
+    } catch (err) {
+      console.warn(`useLocalStorage: failed to write "${key}"`, err)
     }
   }, [key, value])