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/db/db.go

@@ -0,0 +1,50 @@
+package db
+
+import (
+	"database/sql"
+	_ "embed"
+	"fmt"
+	"strings"
+
+	_ "modernc.org/sqlite"
+)
+
+//go:embed migrations/000001_init.up.sql
+var initMigrationUp string
+
+//go:embed migrations/000001_init.down.sql
+var initMigrationDown string
+
+// Connect opens an SQLite database connection with appropriate pragmas
+func Connect(dbPath string) (*sql.DB, error) {
+	dsn := dbPath
+	if !strings.Contains(dsn, "?") {
+		dsn += "?_pragma=foreign_keys(1)&_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)"
+	}
+	db, err := sql.Open("sqlite", dsn)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open database: %w", err)
+	}
+
+	if err := db.Ping(); err != nil {
+		return nil, fmt.Errorf("failed to ping database: %w", err)
+	}
+
+	return db, nil
+}
+
+// RunMigrations applies up migrations
+func RunMigrations(db *sql.DB) error {
+	if _, err := db.Exec(initMigrationUp); err != nil {
+		return fmt.Errorf("failed to apply migration up: %w", err)
+	}
+	return nil
+}
+
+// RollbackMigrations applies down migrations
+func RollbackMigrations(db *sql.DB) error {
+	if _, err := db.Exec(initMigrationDown); err != nil {
+		return fmt.Errorf("failed to apply migration down: %w", err)
+	}
+	return nil
+}