Initial Navis client with NaiveProxy, profiles, ping and git updates

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/sysproxy/sysproxy.go

@@ -0,0 +1,18 @@
+package sysproxy
+
+import "fmt"
+
+// Controller manages OS-level proxy settings.
+type Controller interface {
+	Enable(httpHostPort string) error
+	Disable() error
+	Enabled() bool
+}
+
+// New returns a platform-specific controller.
+func New() Controller {
+	return newPlatform()
+}
+
+// ErrUnsupported is returned on platforms without system proxy support.
+var ErrUnsupported = fmt.Errorf("system proxy is not supported on this platform")