Fix latent lint issues and ensure they're caught in future pipelines

[JesseHerrick]

There were a bunch of lint errors, mainly about not having a return after a fatal error log, that we didn't catch due to the linter only running on the partial set of changes.

This PR:

• Fixes the lint issues.
• Changes the CI so that we always lint the entire codebase, rather than just the diffed files.

---

Note

Low Risk
Test and CI-only changes; no production LSP or indexing behavior is modified.

Overview
Fixes latent golangci-lint issues (mostly missing return after t.Fatal / t.Fatalf in LSP tests) and updates CI so lint always runs on the full repo via make lint (golangci-lint run ./...) instead of the GitHub Action that only covered changed files.

The workflow now installs golangci-lint v2.11.4 with go install and invokes the same path as local development; test-only control-flow tweaks have no runtime impact.

^{Reviewed by Cursor Bugbot for commit ae1f35c. Bugbot is set up for automated code reviews on this repo. Configure here.}