Add CI, and gofmt the eight files it fails on

[nicodes]

This repository had no CI. release.yml was the only workflow — so nothing checked a commit before it became a tag that other repositories download a binary from. fieldsofrevik's setup action pulls a gdlint release and puts it on PATH.

Adding the check immediately found eight unformatted files

src/core/entity_detector.go       src/operations/file_operations.go
src/core/indentation_checker.go   src/operations/remover.go
src/core/pass_analyzer.go         src/optimization/cache.go
src/models/entity.go              src/optimization/parallel.go

They're reformatted in the first commit here rather than a PR of their own, because the two changes are coupled — the CI can't pass without the formatting, and the formatting has no reason to happen without the CI. Every hunk is gofmt's output, no edits of my own, so it reviews as one mechanical change.

What's added

• .github/actions/test — gofmt, vet, go test, build. Called by CI and Release; Release packaged and published without running anything before.
• ci.yml — one job, pull_request + push: [main] (no CD here, so nothing else covers a merge).
• SHA pins and timeout-minutes on both workflows.

On go test

There are no _test.go files, so it reports "no test files" and passes. The step is present rather than omitted so the first test written runs the moment it lands, without anyone remembering to wire it up.

Verified locally: gofmt clean, vet clean, build ok.

Phase 3 of the standardization plan (F10).