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/config/config.go

@@ -409,7 +409,7 @@ var (
 	errNoCertificate = errors.New("holds no PEM certificate")
 	errNotFacility   = errors.New("is not a syslog facility such as local0 or daemon")
 	errNotAppName    = errors.New(
-		"is not 1 to 48 printable ASCII characters without a space, such as gitea")
+		"is not 1 to 48 printable ASCII characters without a space, such as blog")
 	errSetTwice      = errors.New("set only one of them")
 	errNotWebhookURL = errors.New(
 		"is not an http or https URL without a user or a fragment, " +