playground-ng: fix force kill

[breezewish]

What problem does this PR solve?

close #xxx

What is changed and how it works?

• Fix force kill (double Ctrl+C) not working
• Fix stop-all not working in tiup playground-ng:nightly ... suffix

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Details

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 69.56522% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.30%. Comparing base (3a5e13f) to head (42e012d).

Files with missing lines	Patch %	Lines
components/playground-ng/main.go	73.08%	4 Missing and 3 partials ⚠️
components/playground-ng/controller.go	70.00%	3 Missing ⚠️
components/playground-ng/kill_unix.go	66.67%	1 Missing and 1 partial ⚠️
components/playground-ng/shutdown.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2674      +/-   ##
==========================================
+ Coverage   42.29%   42.30%   +0.01%     
==========================================
  Files         423      424       +1     
  Lines       46848    46872      +24     
==========================================
+ Hits        19810    19826      +16     
- Misses      24373    24379       +6     
- Partials     2665     2667       +2     

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-19 14:55:29.857866446 +0000 UTC m=+419357.471823302: ☑️ agreed by xhebox.