feat(kiosk): resolve constant plugin IDs, overrides and the CheckT helper

- kiosk.ReadIdentity: ID()/Requires() as literals or constants across packages and modules, read with go/parser, never run
- plugin minimums from go.mod requires; v0.0.0 is an error, a pseudo-version warns
- kiosk.Validate, kiosk.CheckT (no testing import)
- plugin:add reads IDs through kiosk.ReadIdentity, so const-ID plugins register

modules/kiosk/testdata/other/go.mod

@@ -0,0 +1,7 @@
+module example.test/sm-other-plugin
+
+go 1.27.0
+
+require git.golem15.com/golem15/summercms v0.5.3
+
+replace git.golem15.com/golem15/summercms => ../framework