Refresh brew tap before upgrading in kernel upgrade

[masnwilliams]

Summary

kernel upgrade detects a newer version from GitHub releases, then shells out to brew upgrade kernel/tap/kernel. But brew upgrade doesn't refresh the tap on its own, and Homebrew throttles its auto-update — so right after a release the local tap is stale, brew still sees the old formula, and the upgrade silently no-ops with "already installed" (exit 0). The user sees kernel upgrade announce a new version and then nothing changes.

Repro: release a new version, then on a machine whose tap hasn't refreshed run kernel upgrade → "New version available: X → Y" followed by "Warning: kernel/tap/kernel X already installed", no upgrade.

Fix

• kernel upgrade now runs brew update before brew upgrade kernel/tap/kernel (brew method only; npm/pnpm/bun already pull @latest).
• executeUpgrade/upgradeCommandArgs refactored to run an ordered list of commands so the brew path can do two steps; stderr from all steps is still captured for the existing old-tap error diagnosis.
• The passive suggested-upgrade hint now shows brew update && brew upgrade kernel/tap/kernel for the same reason.

Testing

go build ./..., go vet, gofmt, and go test ./pkg/update/... all pass (suggestion-string test updated).

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Note

Low Risk
CLI-only change to upgrade command sequencing and user-facing hints; no auth, data, or core runtime behavior beyond fixing stale-tap brew upgrades.

Overview
Fixes Homebrew upgrades silently doing nothing right after a release when the local tap is stale: kernel upgrade now runs brew update before brew upgrade kernel/tap/kernel for the brew install path only.

Upgrade execution is refactored so each install method returns an ordered list of shell commands ([][]string). executeUpgrade runs them sequentially and still aggregates stderr across steps for the existing old-tap error handling. Dry-run / displayed commands use brew update && brew upgrade kernel/tap/kernel.

Passive upgrade hints in SuggestUpgradeCommand (brew and unknown-method fallback) use the same two-step brew string. Tests cover brew command ordering and the updated suggestion text.

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[jarugupj]

LGTM

non blocking: for cmd/upgrade.go:103 - could we add a small unit test confirming brew update runs before brew upgrade?

[masnwilliams]

Added cmd/upgrade_test.go — TestUpgradeCommandArgsBrewUpdatesBeforeUpgrade asserts the brew update step precedes brew upgrade for the brew method, plus table coverage of the per-method command args and the display string. go test ./cmd/... green.