core: generate OpenAPI/Swagger docs for all endpoints

[pixels26]

Summary

Adds OpenAPI 3.0 documentation with interactive Swagger UI for all API endpoints, auto-generated from NestJS decorators.

Changes

Configuration

• src/config/swagger.ts — Enhanced Swagger setup: reads version from package.json, adds all 12 API tags with descriptions, JWT Bearer + X-API-Key auth schemes, configurable via SWAGGER_ENABLED env var
• src/main.ts — Production basic auth guard for docs routes using DOCS_USERNAME/DOCS_PASSWORD env vars

Controller decorators

• src/modules/reputation/reputation.controller.ts — Added @UseGuards(JwtAuthGuard), @ApiBearerAuth(), @ApiParam, typed @ApiResponse with ReputationResponseDto; fixed missing auth guard on GET /me
• src/modules/learners/learners.controller.ts — Added @ApiBody({ type: UpdateLearnerProfileDto }) on PATCH endpoint
• src/modules/auth/auth.controller.ts — Added @ApiBody schema for POST /refresh raw parameter

New utilities

• src/common/dto/paginated-response.dto.ts — Reusable PaginationMetaDto and PaginatedResponseDto<T>
• src/common/decorators/api-paginated.decorator.ts — @ApiPaginatedResponse(Model) decorator for paginated endpoints

Routes

• GET /api/v1/docs — Interactive Swagger UI
• GET /api/v1/docs-json — Raw OpenAPI 3.0 spec
• Production: gated behind Basic auth when DOCS_USERNAME/DOCS_PASSWORD are set
• Set SWAGGER_ENABLED=false to disable entirely

Closes #39