fix: log yurt-manager Execute() error before exit

[shiavm006]

Description

• Adds error logging before os.Exit(1) in yurt-manager’s main function.
• When command.Execute() fails, we now log klog.Errorf("yurt-manager failed: %v", err) before exiting.

How I tested it

• go test ./cmd/yurt-manager/...

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 44.08%. Comparing base (ed4eb0a) to head (01457aa).

Files with missing lines	Patch %	Lines
cmd/yurt-manager/yurt-manager.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2504      +/-   ##
==========================================
- Coverage   44.09%   44.08%   -0.01%     
==========================================
  Files         399      399              
  Lines       26554    26555       +1     
==========================================
- Hits        11710    11708       -2     
- Misses      13782    13784       +2     
- Partials     1062     1063       +1     

Flag	Coverage Δ
unittests	44.08% <0.00%> (-0.01%)	⬇️

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[shiavm006]

the test passed locally tho i dont think so it related to the pr

[zyjhtangtang]

@shiavm006 Please pay attention to the inadequate unit test coverage.

[shiavm006]

@shiavm006 Please pay attention to the inadequate unit test coverage.

Regarding unit test coverage main() function is not unit tested, consistent with other entry points in this codebase (e.g., cmd/yurtadm/yurtadm.go). Testing main() functions that call os.Exit() is challenging as it terminates the process, making traditional unit testing impractical.

[shiavm006]

I've manually tested the error logging path, and the underlying command execution is already covered by existing tests @zyjhtangtang