refactor(agent): extract agent pool and HTTP utilities to dedicated package

Moved non-agent-specific logic from agent/pkg/agent/ to internal/agentpool/:
- pool.go: Agent pool management (Get, Add, Remove, List, Iter, etc.)
- http_requests.go: HTTP utilities (health checks, forwarding, websockets, reverse proxy)
- agent.go: Agent struct with HTTP client management

This separates general-purpose pool management from agent-specific configuration,
improving code organization and making the agent package focused on agent config only.

internal/agentpool/pool.go

@@ -0,0 +1,79 @@
+package agentpool
+
+import (
+	"iter"
+	"os"
+	"strings"
+
+	"github.com/puzpuzpuz/xsync/v4"
+	"github.com/yusing/godoxy/agent/pkg/agent"
+)
+
+var agentPool = xsync.NewMap[string, *Agent](xsync.WithPresize(10))
+
+func init() {
+	if strings.HasSuffix(os.Args[0], ".test") {
+		agentPool.Store("test-agent", &Agent{
+			AgentConfig: &agent.AgentConfig{
+				Addr: "test-agent",
+			},
+		})
+	}
+}
+
+func Get(agentAddrOrDockerHost string) (*Agent, bool) {
+	if !agent.IsDockerHostAgent(agentAddrOrDockerHost) {
+		return getAgentByAddr(agentAddrOrDockerHost)
+	}
+	return getAgentByAddr(agent.GetAgentAddrFromDockerHost(agentAddrOrDockerHost))
+}
+
+func GetAgent(name string) (*Agent, bool) {
+	for _, agent := range agentPool.Range {
+		if agent.Name == name {
+			return agent, true
+		}
+	}
+	return nil, false
+}
+
+func Add(cfg *agent.AgentConfig) (added bool) {
+	_, loaded := agentPool.LoadOrCompute(cfg.Addr, func() (*Agent, bool) {
+		return newAgent(cfg), false
+	})
+	return !loaded
+}
+
+func Has(cfg *agent.AgentConfig) bool {
+	_, ok := agentPool.Load(cfg.Addr)
+	return ok
+}
+
+func Remove(cfg *agent.AgentConfig) {
+	agentPool.Delete(cfg.Addr)
+}
+
+func RemoveAll() {
+	agentPool.Clear()
+}
+
+func List() []*Agent {
+	agents := make([]*Agent, 0, agentPool.Size())
+	for _, agent := range agentPool.Range {
+		agents = append(agents, agent)
+	}
+	return agents
+}
+
+func Iter() iter.Seq2[string, *Agent] {
+	return agentPool.Range
+}
+
+func Num() int {
+	return agentPool.Size()
+}
+
+func getAgentByAddr(addr string) (agent *Agent, ok bool) {
+	agent, ok = agentPool.Load(addr)
+	return agent, ok
+}