Remove everything specific to a Gitea deployment (closes #209)

Delete the Gitea compose setup, its document, its two scripts and their
make targets. Drop the Core Rule Set exclusions written for Gitea: the
ten query parameters skipped by rules 930120, 932160 and 932260, and the
gitea_flash and redirect_to cookies. The remaining changes are
renumbered, five in all. Documents and tests use neutral examples.

Model: opus-5-5

internal/servewaf/coreruleset_test.go

@@ -179,7 +179,7 @@ func TestAnomalyThreshold(t *testing.T) {
 	s.request(client, sqlInjection, http.StatusForbidden, requestlog.ActionWAFBlocked)
 }
 
-func TestDisabledRulesSwitchOffWhatGiteaWouldBeRefused(t *testing.T) {
+func TestDisabledRulesSwitchOffWhatACodeForgeWouldBeRefused(t *testing.T) {
 	t.Parallel()
 
 	for _, request := range []struct {