fix(frontend): clear TypeScript strict-mode errors

- vite-env.d.ts now declares ImportMetaEnv with the three VITE_*
  variables the project uses, restoring proper typing for
  import.meta.env in apiClient.ts.
- QualityFlag.tsx widens its 'flags' prop to accept the domain
  QualityFlags type, the loose Record form used in mocks, or null,
  ending the structural-mismatch errors at five callsites
  (DocumentsPage, DocumentViewerPage, QualityControlPage,
  ChunkPreview, SearchResultCard).
- DashboardPage trend callbacks are typed against DashboardStats so
  the implicit-any complaints disappear without weakening intent.

npx tsc --noEmit -> clean. vite build -> ok.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/pages/DashboardPage.tsx

@@ -1,5 +1,6 @@
 import { FileText, Layers, ShieldAlert, Sparkles, Cpu, Database } from "lucide-react";
 
+import type { DashboardStats } from "@/services/types";
 import { PageHeader } from "@/components/common/PageHeader";
 import { Button } from "@/components/ui/button";
 import { KpiCard } from "@/widgets/KpiCard";
@@ -39,7 +40,7 @@ export function DashboardPage() {
           delta={4.2}
           icon={<FileText className="h-4 w-4" />}
           tone="primary"
-          trend={data?.daily_ingest.slice(-12).map((d) => d.ingested) ?? []}
+          trend={data?.daily_ingest.slice(-12).map((d: DashboardStats["daily_ingest"][number]) => d.ingested) ?? []}
         />
         <KpiCard
           label="OCR confidence"
@@ -48,7 +49,7 @@ export function DashboardPage() {
           delta={1.3}
           icon={<Layers className="h-4 w-4" />}
           tone="success"
-          trend={data?.ocr_distribution.map((d) => d.count) ?? []}
+          trend={data?.ocr_distribution.map((d: DashboardStats["ocr_distribution"][number]) => d.count) ?? []}
         />
         <KpiCard
           label="Needs manual review"