feat(openflare): migrate of_node_access_logs to ClickHouse

Move node access log storage from PostgreSQL/SQLite to ClickHouse
(database: openflare). System startup now requires a healthy ClickHouse
connection and auto-initializes the schema. Agent heartbeat writes access
logs via batch insert; goose migration drops the legacy relational table.

openflare-server/internal/db/clickhouse_schema.go

@@ -0,0 +1,51 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package db
+
+import (
+	"context"
+	"fmt"
+	"log"
+)
+
+const openFlareNodeAccessLogsDDL = `
+CREATE TABLE IF NOT EXISTS of_node_access_logs
+(
+    id          UInt64,
+    node_id     String,
+    logged_at   DateTime64(3, 'UTC'),
+    remote_addr String,
+    region      String,
+    host        String,
+    path        String,
+    status_code Int32,
+    created_at  DateTime64(3, 'UTC')
+)
+ENGINE = MergeTree()
+PARTITION BY toYYYYMM(logged_at)
+ORDER BY (node_id, logged_at, remote_addr, host, path, status_code)
+SETTINGS index_granularity = 8192`
+
+// EnsureClickHouseSchema creates the openflare database and required tables.
+func EnsureClickHouseSchema(ctx context.Context) error {
+	if ChConn == nil {
+		return fmt.Errorf("clickhouse connection is not initialized")
+	}
+
+	if err := ChConn.Exec(ctx, "CREATE DATABASE IF NOT EXISTS openflare"); err != nil {
+		return fmt.Errorf("create database openflare: %w", err)
+	}
+	if err := ChConn.Exec(ctx, openFlareNodeAccessLogsDDL); err != nil {
+		return fmt.Errorf("create table of_node_access_logs: %w", err)
+	}
+	return nil
+}
+
+func ensureClickHouseSchemaOnStartup() {
+	ctx := context.Background()
+	if err := EnsureClickHouseSchema(ctx); err != nil {
+		log.Fatalf("[ClickHouse] ensure schema failed: %v\n", err)
+	}
+	log.Println("[ClickHouse] schema ready (database: openflare)")
+}