🔧 fix: go vet check now actually works

[jpmcb]

Gets the go vet check to actually work via go vet ./... - also adds some fixture checks for the go module

Refs PCC-1166

[greptile-apps]

Greptile Summary

The PR broadens the Go vet check to inspect every package under the supplied module and adds a minimal fixture-based Make target for exercising the Go checks.

• Changes CheckGoVet to execute go vet ./....
• Adds a fixture Go module and Make target covering module-tidiness and vet checks.
• Refreshes several direct and indirect Go dependencies and their checksums.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete changed-code failures identified.

The expanded vet command runs from the mounted module root and covers nested packages, while the new fixture provides a valid module for both checks; investigated dependency advisories either predate this PR or have no reachable affected path in repository code.

Important Files Changed

Filename	Overview
go/main.go	Updates the vet invocation to cover all packages under the mounted source module; no actionable defect was identified.
go/Makefile	Adds fixture commands for exercising both Go module tidiness and vet checks.
go/fixtures/go.mod	Defines the minimal Go 1.26 fixture module used by the new Make target.
go/go.mod	Refreshes dependency versions without introducing a reachable compatibility or security defect identified in this review.

_{Reviews (1): Last reviewed commit: "🔧 fix: go vet check now actually works" | Re-trigger Greptile}

[linear-code]

PCC-1166