refactor(edge): Server 协议统一与 wsclient 收敛（Phase 3 Batch 3）

- openflare/agent/relay/flared 协议类型改为 pkg/protocol 别名，删除重复 struct
- 新增 edge/wsclient Preset 表，三组件 wsclient 改为薄包装
- 更新设计文档、计划与 changelog

internal/apps/edge/wsclient/client_test.go

@@ -0,0 +1,66 @@
+package wsclient
+
+import (
+	"testing"
+	"time"
+)
+
+func TestPresetConfig(t *testing.T) {
+	tests := []struct {
+		preset    Preset
+		headerKey string
+		wsPath    string
+	}{
+		{preset: PresetAgent, headerKey: "X-Agent-Token", wsPath: "/api/v1/agent/ws"},
+		{preset: PresetRelay, headerKey: "X-Agent-Token", wsPath: "/api/v1/relay/ws"},
+		{preset: PresetFlared, headerKey: "X-Tunnel-Token", wsPath: "/api/v1/tunnel/ws"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.wsPath, func(t *testing.T) {
+			if got := PresetHeaderKey(tt.preset); got != tt.headerKey {
+				t.Fatalf("PresetHeaderKey() = %q, want %q", got, tt.headerKey)
+			}
+			if got := PresetWSPath(tt.preset); got != tt.wsPath {
+				t.Fatalf("PresetWSPath() = %q, want %q", got, tt.wsPath)
+			}
+		})
+	}
+}
+
+func TestClientURL(t *testing.T) {
+	tests := []struct {
+		name    string
+		preset  Preset
+		baseURL string
+		want    string
+	}{
+		{
+			name:    "agent https",
+			preset:  PresetAgent,
+			baseURL: "https://example.com",
+			want:    "wss://example.com/api/v1/agent/ws",
+		},
+		{
+			name:    "relay http with path prefix",
+			preset:  PresetRelay,
+			baseURL: "http://example.com/api",
+			want:    "ws://example.com/api/api/v1/relay/ws",
+		},
+		{
+			name:    "flared wss",
+			preset:  PresetFlared,
+			baseURL: "wss://edge.example.com",
+			want:    "wss://edge.example.com/api/v1/tunnel/ws",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			client := New(tt.preset, tt.baseURL, "token", time.Second)
+			if got := client.URL(); got != tt.want {
+				t.Fatalf("URL() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}