Resolve outstanding `mage lint` findings

### Summary

Resolve the outstanding `golangci-lint` findings reported by `mage lint` on `main`.

Current findings*

```shell
487 issues:
* asciicheck: 1
* bodyclose: 3
* depguard: 6
* errcheck: 50
* errorlint: 15
* forbidigo: 17
* goimports: 3
* gomodguard_v2: 1
* gosec: 50
* govet: 17
* ineffassign: 12
* misspell: 23
* modernize: 50
* nakedret: 12
* nilerr: 4
* noctx: 41
* nolintlint: 25
* staticcheck: 50
* testifylint: 50
* unconvert: 3
* unused: 50
* wastedassign: 4
```

* Unsure if precise. `golangci-lint` crashed when trying to run locally.

### Criteria for completion

- [ ] All current reported findings are addressed.
- [ ] `mage lint` exits 0 on `main` (no findings, no panics).
- [ ] No new `//nolint:` annotations introduced unless accompanied by an explanatory comment per the `nolintlint` rule.

Start by running `mage lint` on `main` and review the reported findings grouped by linter; the issue lists the current categories and counts but no specific files. Address the findings without unexplained `//nolint:` annotations, then rerun `mage lint` until it exits 0 without findings or panics.

Written by the indexing model from the issue text.