Fix production build: npm registry flakiness, stray package-lock.json dir, TS error

- registry.npmjs.org was intermittently ETIMEDOUT mid-download from this
  host; switched to registry.npmmirror.com (also raised npm's own retry
  budget as a second line of defense).
- frontend/package-lock.json on disk was actually an empty directory
  (untracked, root-owned — a stray artifact, likely from an old bad
  bind-mount), which broke `COPY . .` once npm install got past it.
- documents/page.tsx had a real type error (selectedItem.file narrowing
  didn't survive into the .map() closure) that `next dev` never
  surfaced but `next build`'s stricter check does — fixed by hoisting
  the narrowed array into selectedFiles once instead of re-narrowing
  selectedItem.file at each use.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gh2UXUQUVBWroWEnn1FLFG

frontend/Dockerfile

@@ -9,7 +9,14 @@ WORKDIR /app
 ENV NODE_OPTIONS=--dns-result-order=ipv4first
 
 COPY package.json package-lock.json* ./
-RUN npm install
+# registry.npmjs.org itself is unreliable from this host (mid-download
+# stalls even with aggressive npm retries) — route through npmmirror.com
+# instead, which is consistently reachable from this network.
+RUN npm config set registry https://registry.npmmirror.com && \
+    npm config set fetch-retries 8 && \
+    npm config set fetch-retry-mintimeout 20000 && \
+    npm config set fetch-retry-maxtimeout 120000 && \
+    npm install
 
 COPY . .
 RUN npm run build

frontend/app/documents/page.tsx

@@ -47,6 +47,7 @@ export default async function DocumentsPage({
   // Логика определения конкретного файла для отображения
   let fileForLink: string | null = null;
   let previewUrl: string | null = null;
+  const selectedFiles: string[] | null = Array.isArray(selectedItem?.file) ? selectedItem.file : null;
 
   if (selectedItem?.file) {
     if (Array.isArray(selectedItem.file)) {
@@ -125,16 +126,16 @@ export default async function DocumentsPage({
                   <h2>{selectedItem?.title ?? "Документ не выбран"}</h2>
                   
                   {/* Вывод списка кнопок, если файлов несколько */}
-                  {selectedItem?.file && Array.isArray(selectedItem.file) && selectedItem.file.length > 1 && (
+                  {selectedFiles && selectedFiles.length > 1 && (
                     <div style={{ display: "flex", gap: "8px", flexWrap: "wrap", marginTop: "12px" }}>
-                      {selectedItem.file.map((fileName, idx) => {
+                      {selectedFiles.map((fileName, idx) => {
-                        const validCurrentIndex = selectedIndex < selectedItem.file.length ? selectedIndex : 0;
+                        const validCurrentIndex = selectedIndex < selectedFiles.length ? selectedIndex : 0;
                         const isActive = validCurrentIndex === idx;
-                        
+
                         return (
                           <Link
                             key={fileName}
-                            href={`/documents?doc=${selectedItem.id}&fileIndex=${idx}`}
+                            href={`/documents?doc=${selectedItem?.id}&fileIndex=${idx}`}
                             className={`documents-link documents-link--button ${
                               isActive ? "documents-link--active" : ""
                             }`}