refactor(api): restructured API for type safety, maintainability and docs generation

- These changes makes the API incombatible with previous versions
- Added new types for error handling, success responses, and health checks.
- Updated health check logic to utilize the new types for better clarity and structure.
- Refactored existing handlers to improve response consistency and error handling.
- Updated Makefile to include a new target for generating API types from Swagger.
- Updated "new agent" API to respond an encrypted cert pair

internal/api/v1/auth/check.go

@@ -0,0 +1,19 @@
+package auth
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/yusing/go-proxy/internal/auth"
+)
+
+// @x-id				"check"
+// @Base			/api/v1
+// @Summary		Check authentication status
+// @Description	Checks if the user is authenticated by validating their token
+// @Tags			auth
+// @Produce		plain
+// @Success		200	{string}	string	"OK"
+// @Failure		403	{string}	string	"Forbidden: use X-Redirect-To header to redirect to login page"
+// @Router			/auth/check [head]
+func Check(c *gin.Context) {
+	auth.AuthCheckHandler(c.Writer, c.Request)
+}