deploy/gitea: Gitea behind traefik, rproxy and servewaf, with its test (closes #178)

A compose setup that runs gitea 1.27.3 behind traefik, rproxy and servewaf on one shared network with IPv4 and IPv6, and `script/gitea-setup` (`make gitea-setup`), which brings it up and checks that a page load, a push and a clone pass through rproxy and are checked by servewaf. Containers on the shared network skip servewaf's checks; the gateways do not. gitea gets a secret key made per install and has sign-up off. `docs/gitea.md` explains each setting.

Judgement call: the Core Rule Set runs in `detect` mode here until #198 lands.

Model: deepseek-v4-pro (implementation), opus-5-5 (rework)

Makefile

@@ -1,12 +1,13 @@
 .PHONY: bootstrap setup test lint fmt fmt-check tidy check docker hooks build \
-	run example-app gitea-requests
+	run example-app gitea-requests gitea-setup
 
 # Makefile targets are thin shims; the implementations live in script/
 # per the scripts-to-rule-them-all pattern (see the Entrypoints section
 # of README.md). tidy writes go.mod and go.sum as `go mod tidy` does,
 # which test checks. build and run are for working on the code by hand;
 # example-app checks the image with an app built on it; gitea-requests
-# reports the gitea requests the Core Rule Set refuses at the defaults.
+# reports the gitea requests the Core Rule Set refuses at the defaults;
+# gitea-setup checks the setup in deploy/gitea.
 
 bootstrap:
 	@script/bootstrap
@@ -49,3 +50,6 @@ example-app:
 
 gitea-requests:
 	@script/gitea-requests
+
+gitea-setup:
+	@script/gitea-setup