Format Go with gofmt, then golines -m 77 (closes #160)

REPO_POLICIES names gofmt then golines -m 77 as the Go formatter, says
what script/fmt, script/fmt-check and script/bootstrap do, and pins
golines v0.13.0 by commit hash. The Go style guide and both checklists
agree. lll stays at 88: golines leaves long strings and comments alone.

Model: opus-5-5

prompts/EXISTING_REPO_CHECKLIST.md

@@ -261,8 +261,8 @@ with your task.
 
 - [ ] Platform-standard formatter is configured (`black`, `prettier`, and for Go
       `gofmt` then `golines -m 77`)
-- [ ] Default formatter config, except four-space indents (not Go),
+- [ ] Default formatter config, except four-space indents (not Go) and the Go
-      `proseWrap: always` for Markdown, and the Go 77-column limit
+      77-column limit
 - [ ] Go: `script/bootstrap` installs `golines` with `go install` pinned to a
       commit hash; `script/fmt-check` fails when `gofmt` or `golines -m 77`
       would change a file

prompts/REPO_POLICIES.md

@@ -692,11 +692,6 @@ style conventions are in separate documents:
     go install github.com/segmentio/golines@8f32f0f7e89c30f572c7f2cd3b2a48016b9d8bbf
     ```
 
-    `script/bootstrap` reads the installed version from the `mod` line of
-    `go version -m "$(command -v golines)"`, which reports `v0.13.0`. It does
-    not use `golines --version`, which prints `golines vdev` for a binary that
-    `go install` built.
-
     `golines` cannot shorten every line: long string literals and comments stay
     as they are. golangci-lint's `lll` limit therefore stays at 88 columns, so
     it fails only lines far past the formatter's limit.