feat(api): add GetContainer endpoint for Docker container retrieval

- Implemented GetContainer function to retrieve container details by ID.
- Added error handling for missing ID, container not found, and client creation failures.
- Enhanced Container struct to support omitempty for state field in JSON responses.
- Updated API documentation with Swagger annotations for the new endpoint.

internal/api/v1/docker/container.go

@@ -0,0 +1,63 @@
+package dockerapi
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	apitypes "github.com/yusing/go-proxy/internal/api/types"
+	"github.com/yusing/go-proxy/internal/docker"
+)
+
+// @x-id				"container"
+// @BasePath		/api/v1
+// @Summary		Get container
+// @Description	Get container by container id
+// @Tags			docker
+// @Produce		json
+// @Param			id	path		string	true	"Container ID"
+// @Success		200	{object}		Container
+// @Failure		400	{object}	apitypes.ErrorResponse "ID is required"
+// @Failure		403	{object}	apitypes.ErrorResponse
+// @Failure		404	{object}	apitypes.ErrorResponse "Container not found"
+// @Failure		500	{object}	apitypes.ErrorResponse
+// @Router			/docker/container/{id} [get]
+func GetContainer(c *gin.Context) {
+	id := c.Param("id")
+	if id == "" {
+		c.JSON(http.StatusBadRequest, apitypes.Error("id is required"))
+		return
+	}
+
+	dockerHost, ok := docker.GetDockerHostByContainerID(id)
+	if !ok {
+		c.JSON(http.StatusNotFound, apitypes.Error("container not found"))
+		return
+	}
+
+	client, err := docker.NewClient(dockerHost)
+	if err != nil {
+		c.Error(apitypes.InternalServerError(err, "failed to create docker client"))
+		return
+	}
+
+	defer client.Close()
+
+	cont, err := client.ContainerInspect(c.Request.Context(), id)
+	if err != nil {
+		c.Error(apitypes.InternalServerError(err, "failed to inspect container"))
+		return
+	}
+
+	var state ContainerState
+	if cont.State != nil {
+		state = cont.State.Status
+	}
+
+	c.JSON(http.StatusOK, &Container{
+		Server: dockerHost,
+		Name:   cont.Name,
+		ID:     cont.ID,
+		Image:  cont.Image,
+		State:  state,
+	})
+}

internal/api/v1/docker/containers.go

@@ -16,7 +16,7 @@ type Container struct {
 	Name   string         `json:"name"`
 	ID     string         `json:"id"`
 	Image  string         `json:"image"`
-	State  ContainerState `json:"state"`
+	State  ContainerState `json:"state,omitempty" extensions:"x-nullable"`
 } // @name ContainerResponse
 
 // @x-id				"containers"