Add authoritative URLs to checklists and copy .golangci.yml

- Add .golangci.yml from upaas as authoritative copy in this repo
- Update REPO_POLICIES.md to reference .golangci.yml by URL
- Add fetch URLs for all template files in both checklists:
  .gitignore, .editorconfig, Makefile, .prettierrc, .prettierignore,
  REPO_POLICIES.md, .golangci.yml, check.yml

prompts/EXISTING_REPO_CHECKLIST.md

@@ -23,16 +23,23 @@ with your task.
 - [ ] `.gitignore` is comprehensive (OS, editor, language artifacts, secrets) —
       fetch from `https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitignore`
       if missing
-- [ ] `.editorconfig` exists
+- [ ] [`.editorconfig`](https://git.eeqj.de/sneak/prompts/raw/branch/main/.editorconfig)
+      exists
 - [ ] `Dockerfile` and `.dockerignore` exist; Dockerfile runs `make check` as a
       build step
 - [ ] Gitea Actions workflow in `.gitea/workflows/` runs `docker build .` on
-      push
+      push — reference
+      [check.yml](https://git.eeqj.de/sneak/prompts/raw/branch/main/.gitea/workflows/check.yml)
 - [ ] Language-specific config:
-    - [ ] Go: `go.mod`, `go.sum`, `.golangci.yml`
-    - [ ] JS: `package.json`, `yarn.lock`, `.prettierrc`, `.prettierignore`
+    - [ ] Go: `go.mod`, `go.sum`,
+          [`.golangci.yml`](https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml)
+    - [ ] JS: `package.json`, `yarn.lock`,
+          [`.prettierrc`](https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierrc),
+          [`.prettierignore`](https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierignore)
     - [ ] Python: `pyproject.toml`
-    - [ ] Docs/writing: `.prettierrc`, `.prettierignore`
+    - [ ] Docs/writing:
+          [`.prettierrc`](https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierrc),
+          [`.prettierignore`](https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierignore)
 
 ## Makefile