Compact REPO_POLICIES.md without losing rules (closes #158)

The rules now sit under headings, the pinning rule first. Each rule that
was stated in several places is stated once. From 1,145 lines and 8,427
words to 1,012 lines and 7,709 words. Code blocks are unchanged, except
that the Makefile copies of the Go and Python test commands are gone:
the Dockerfile examples carry the same commands.

Both checklists name the `.golangci.yml` section.

Model: fable-5-1

prompts/EXISTING_REPO_CHECKLIST.md

@@ -163,7 +163,7 @@ with your task.
     - [ ] Go: `go.mod`, `go.sum`, `.golangci.yml` (fetch from
           `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml` and,
           in the same commit, set the lint phase digest to the one named in the
-          `.golangci.yml` paragraph of `REPO_POLICIES.md`)
+          `.golangci.yml` section of `REPO_POLICIES.md`)
     - [ ] JS: `package.json`, `yarn.lock`, `.yarnrc.yml`, `.yarn/releases/`,
           `.gitattributes`, `.prettierrc`, `.prettierignore` (fetch the last two
           from `https://git.eeqj.de/sneak/prompts/raw/branch/main/.prettierrc`

prompts/NEW_REPO_CHECKLIST.md

@@ -180,7 +180,7 @@ Template files can be fetched from:
     - [ ] Go: `go mod init sneak.berlin/go/<name>`, `.golangci.yml` (fetch from
           `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml` and,
           in the same commit, set the lint phase digest to the one named in the
-          `.golangci.yml` paragraph of `REPO_POLICIES.md`)
+          `.golangci.yml` section of `REPO_POLICIES.md`)
     - [ ] JS, or any repository that runs prettier through yarn: make the first
           `yarn.lock` with the steps below. `script/bootstrap` installs no yarn
           until `yarn.lock` exists, so run them with any distribution's node and