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/.env.example

@@ -0,0 +1,19 @@
+# ==============================================================================
+# AI Agent Networking Lab (ANL) Backend API Server Configuration
+# ==============================================================================
+
+# Server binding host and port
+HOST=0.0.0.0
+PORT=8080
+
+# SQLite database file path (Inside container: /app/data/anl.db)
+DB_PATH=anl.db
+
+# Gin runtime mode: release | debug | test
+GIN_MODE=release
+
+# Allowed CORS Origins (Comma separated, or * for all)
+CORS_ALLOW_ORIGINS=*
+
+# Automatically run SQL schema migrations on startup (true | false)
+AUTO_MIGRATE=true