Sync wordy with problem specifications

[ManasDasri]

Adds four canonical test cases missing from the wordy suite: 'just a zero', 'just a negative number', 'addition with a left hand zero', and 'addition with a right hand zero'. All pure additions, no reimplements involved. No changes to Example.vb needed - the existing regex-based solution already handles zero and negative-number inputs correctly.

Verified via pwsh ./bin/test.ps1 wordy - all tests pass.

Closes #512

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