man: remove tools.go in favor of tools directive

[thaJeztah]

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[codecov-commenter]

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✅ All modified and coverable lines are covered by tests.

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[docker-agent]

Assessment: 🟢 APPROVE

This PR modernizes the Docker CLI's tool dependency management by replacing the legacy //go:build tools blank-import pattern (man/tools.go) with Go 1.25's native tool directive in vendor.mod.

Changes reviewed:

• man/tools.go — deleted: the old //go:build tools / blank-import file for go-md2man/v2 is superseded by the tool directive on Go ≥ 1.21 (and fully supported in 1.25).
• vendor.mod — github.com/cpuguy83/go-md2man/v2 added to a grouped tool (...) block and moved from the direct require section to // indirect (correct: the // indirect annotation for tool-only dependencies is the expected Go modules behaviour when no production code imports the package).

No issues found. The grouped tool (...) syntax is valid in Go 1.25, the // indirect marking is semantically correct for tool-only deps, and go mod vendor will continue to vendor the tool sources via the directive. Removal of the man/tools.go file is safe given the project requires Go 1.25+.