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

Makefile

@@ -1,13 +1,11 @@
 .PHONY: bootstrap setup test lint fmt fmt-check tidy check docker hooks build \
-	run example-app gitea-requests gitea-setup
+	run example-app
 
 # 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;
-# gitea-setup checks the setup in deploy/gitea.
+# example-app checks the image with an app built on it.
 
 bootstrap:
 	@script/bootstrap
@@ -47,9 +45,3 @@ run:
 
 example-app:
 	@script/example-app
-
-gitea-requests:
-	@script/gitea-requests
-
-gitea-setup:
-	@script/gitea-setup