feat(browser): add POST /open with session restore and reader mode

- restores cookies and localStorage from DB before page navigation
- readerMode flag extracts plain text via @mozilla/readability (Firefox reader engine)
- add localStorage default '{}' on session entity for clean schema migrations

src/browser/dto/open.dto.ts

@@ -0,0 +1,26 @@
+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+import { IsBoolean, IsOptional, IsString, IsUrl } from 'class-validator';
+
+export class OpenDto {
+  @ApiProperty({
+    description: 'Session name previously created by POST /login',
+    example: 'test-session-1',
+  })
+  @IsString()
+  sessionName: string;
+
+  @ApiProperty({
+    description: 'URL to open with the authenticated session',
+    example: 'https://cabinet-liquio-diia-stg.kitsoft.ua/messages',
+  })
+  @IsUrl({ require_tld: true, require_protocol: true })
+  url: string;
+
+  @ApiPropertyOptional({
+    description: 'When true, return a plain-text reader-mode summary instead of raw HTML',
+    default: false,
+  })
+  @IsOptional()
+  @IsBoolean()
+  readerMode?: boolean;
+}