fix: address lipgloss styling gaps

[srtaalej]

Summary

• Fix Warning() rendering in slackGreen instead of slackYellow under the charm experiment
• Migrate last Styler().Red()/Styler().Green() calls in cmd/sandbox/list.go to
  style.Red()/style.Green()

Context

Follow-up from PR #365 (charm-lipgloss-migration) addressing deferred review feedback.

Test plan

• Run go test ./internal/style/... ./cmd/sandbox/... — all pass
• Verify Warning() renders yellow (not green) with charm enabled
• Verify sandbox list status colors (red for archived, green for active) render correctly

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.00%. Comparing base (ca87f1d) to head (1393151).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #391 +/- ##
==========================================
+ Coverage 66.97% 67.00% +0.03% 
==========================================
Files 218 218 Lines 18090 18090 ==========================================
+ Hits 12116 12122 +6 + Misses 4837 4831 -6 
Partials 1137 1137 

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[mwbrooks]

✅ Looks good on my side! 💅🏻