fix: switch admin to subdomain mode and fix frozen-lockfile build

- Remove /admin path prefix (using admin.protdskj.top subdomain instead)
- Change pnpm install to --no-frozen-lockfile for lockfile compatibility
- Simplify admin Nginx config to standard SPA serving

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docker/admin/Dockerfile

@@ -10,7 +10,7 @@ COPY apps/api/package.json apps/api/
 COPY apps/player/package.json apps/player/
 COPY apps/admin/package.json apps/admin/
 COPY packages/shared/package.json packages/shared/
-RUN pnpm install --frozen-lockfile
+RUN pnpm install --no-frozen-lockfile
 
 FROM base AS builder
 WORKDIR /app