The linter config, .gitignore and .dockerignore from the current templates (closes #40)

.golangci.yml is now a byte-identical copy of the sneak/prompts next
copy: depguard is on with the test-support rule, and the gomodguard_v2
block list is in. keyfunc has no test-support packages of its own, so
the deny list is left as it is.

.gitignore and .dockerignore are the sneak/prompts next copies with this
repo's own entries added at the end: /keyfunc in both, and .gitea in
.dockerignore. .git stays in the Docker build context without
.git/config, for the version stamp.

The README TODO line for this issue is removed.

Model: opus-5-5

README.md

@@ -313,7 +313,6 @@ The open issues that stand between the tree and a 1.0 release:
 
 - [#38 Lint and test as phases of the Dockerfile, as the current repo policy requires](https://git.eeqj.de/sneak/keyfunc/issues/38)
 - [#39 make fmt and make fmt-check cover Markdown with prettier](https://git.eeqj.de/sneak/keyfunc/issues/39)
-- [#40 The linter config, .gitignore and .dockerignore from the current templates](https://git.eeqj.de/sneak/keyfunc/issues/40)
 - [#42 go-bip39 no longer exists upstream: keep it, or copy it into the repo?](https://git.eeqj.de/sneak/keyfunc/issues/42)
 
 ## License