feat(backend,docker,docs): implement Go/Gin/SQLite REST API server, Docker containerization, and architecture specifications

- Implement standalone Go backend API server using Gin and pure-Go SQLite (modernc.org/sqlite)
- Add 11-table schema DDL migrations (000001_init.up.sql) based on DATA_TABLE.md
- Add seed data ingestion tool (cmd/seed) and static TypeScript content exporter (cmd/export-content)
- Add configuration loader (internal/config) supporting environment variables and .env files (HOST, PORT, DB_PATH, GIN_MODE, CORS_ALLOW_ORIGINS, AUTO_MIGRATE)
- Add lightweight multi-stage Dockerfile and docker-compose.yml with persistent SQLite volume
- Add comprehensive architecture specification (ARCHITECTURE.md) and REST API interface specification (API_INTERFACE.md)
- Harmonize frontend publications page to consume isHighlight flag from database-synced content

backend/internal/httpx/response.go

@@ -0,0 +1,45 @@
+package httpx
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+type ErrorDetail struct {
+	Message string `json:"message"`
+}
+
+type ErrorResponse struct {
+	Error ErrorDetail `json:"error"`
+}
+
+type SuccessResponse struct {
+	Data any `json:"data"`
+}
+
+func OK(c *gin.Context, data any) {
+	c.JSON(http.StatusOK, SuccessResponse{
+		Data: data,
+	})
+}
+
+func Error(c *gin.Context, status int, msg string) {
+	c.JSON(status, ErrorResponse{
+		Error: ErrorDetail{
+			Message: msg,
+		},
+	})
+}
+
+func BadRequest(c *gin.Context, msg string) {
+	Error(c, http.StatusBadRequest, msg)
+}
+
+func NotFound(c *gin.Context, msg string) {
+	Error(c, http.StatusNotFound, msg)
+}
+
+func InternalServerError(c *gin.Context, msg string) {
+	Error(c, http.StatusInternalServerError, msg)
+}