ci: add gofmt + go vet lint gate to Run Tests

[vks-team]

Summary

Item #3 of the CLI-flow alignment. Adds a lightweight lint job to run-tests.yml:

• gofmt formatting check (fails if any file isn't gofmt-formatted)
• go vet across the module

Both already pass repo-wide (verified), so this just locks in the current state as a per-PR gate. CI previously only built + tested; there was no style/vet gate.

Kept deliberately conservative — a fuller golangci-lint (errcheck/staticcheck/…) can follow once the team triages its findings on this never-linted codebase (adding it blind would flood).

Branch protection

After merge, a new check context lint appears — add it to main's required status checks alongside the build (...) legs and title.

Plan status (final)

• ci: add develop branch to test workflows, update development guide #1 scaffold (feat: scaffold command for new product CLIs #32) · docs: add CONTRIBUTING, CODE_OF_CONDUCT, issue/PR templates, dependabot #2 conventions (test(cmd): enforce cross-product CLI conventions #33) · feat: add logo to documentation site #6 release-please (ci: adopt release-please for commit-driven versioning #34) — merged
• feat: add MkDocs documentation site with GitHub Pages #4/fix: correct upload-pages-artifact action name #5 per-product CLAUDE.md + skills (docs: per-product CLAUDE.md (tier 2) and agent skills #35)
• build(deps-dev): update setuptools requirement from >=68.0 to >=82.0.1 #3 lint gate (this PR)