Remove what is about deploying behind Gitea (closes #209)

Delete the Gitea compose setup, its document, its two scripts and their
make targets. Documents and tests no longer use Gitea as the example
deployment. The Core Rule Set exclusions for Gitea's false positives in
internal/waf stay, with their comments and tests.

Model: opus-5-5

internal/servewaf/alerts_test.go

@@ -18,7 +18,7 @@ const (
 	alertWebhookURL = "SWWAF_ALERT_WEBHOOK_URL"
 	alertMaxPerHour = "SWWAF_ALERT_MAX_PER_HOUR"
 	// alertInstance is the instance every alert of these tests gives.
-	alertInstance = "fsn1app1/gitea"
+	alertInstance = "fsn1app1/blog"
 )
 
 func TestBanForABrokenLimitRaisesABanAlertWithItsNotes(t *testing.T) {