feat(mcp): 设置 → MCP 子页 + 策略 API + 官网/文档接入

借鉴 DBX：安装检测（Node/npm/包/Go 二进制）、只读与 allow_dangerous、
连接白名单、多客户端配置片段；GET/PUT /api/ai/mcp-policy、/mcp-install；
文档 /docs/mcp 与落地页 AI/MCP 块；对照 docs/16 勾选设置项、列仍未完清单。

server/internal/aitools/policy_test.go

@@ -0,0 +1,68 @@
+package aitools
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestSaveLoadPolicyRoundTrip(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("HOME", dir)
+	// PolicyPath uses UserHomeDir → ~/.opsxdb/mcp.json
+	p := Policy{
+		AllowedConnectionIDs: []string{" a ", "b", "a", ""},
+		Mode:                 "READ_WRITE",
+		AllowDangerous:       true,
+		DefaultLimit:         50,
+		MaxLimit:             200,
+	}
+	if err := SavePolicy(p); err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(dir, ".opsxdb", "mcp.json")
+	if _, err := os.Stat(path); err != nil {
+		t.Fatal(err)
+	}
+	got, err := LoadPolicy()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Mode != ModeReadWrite {
+		t.Fatalf("mode=%s", got.Mode)
+	}
+	if !got.AllowDangerous {
+		t.Fatal("want allow_dangerous")
+	}
+	if len(got.AllowedConnectionIDs) != 2 || got.AllowedConnectionIDs[0] != "a" || got.AllowedConnectionIDs[1] != "b" {
+		t.Fatalf("ids=%v", got.AllowedConnectionIDs)
+	}
+	if got.DefaultLimit != 50 || got.MaxLimit != 200 {
+		t.Fatalf("limits %d/%d", got.DefaultLimit, got.MaxLimit)
+	}
+}
+
+func TestDangerousSQLRequiresAllowFlag(t *testing.T) {
+	rt := NewRuntime(Policy{
+		AllowedConnectionIDs: []string{"c1"},
+		Mode:                 ModeReadWrite,
+		AllowDangerous:       false,
+	})
+	rt.FindConn = func(id string) (*SavedConnection, error) {
+		return &SavedConnection{ID: id, Name: "c1", Driver: "mysql", Host: "127.0.0.1", Port: 3306}, nil
+	}
+	rt.Audit = func(AuditEntry) {}
+	rt.AllowConfirmedWrite = true
+	_, err := rt.Call(context.Background(), ToolExecuteQuery, map[string]any{
+		"connection_id":  "c1",
+		"sql":            "DROP TABLE users",
+		"confirm_danger": true,
+	})
+	if err == nil || !contains(err.Error(), "dangerous sql disabled") {
+		t.Fatalf("want dangerous disabled, got %v", err)
+	}
+}
+
+func contains(s, sub string) bool { return strings.Contains(s, sub) }