fix: exclude build output from coverage

[marcolink]

Summary

• restrict Jest coverage collection to source files under src/**
• ignore generated lib/** output during coverage runs
• remove redundant build step before coverage upload in CI

Why

The Apr 1 CI change started running pnpm build before pnpm test:coverage. That generated lib/**, and Jest/Coveralls began counting both source and compiled output, dropping reported coverage from about 90% to about 56%.

Verification

• pnpm exec jest --coverage --coverageReporters=text-summary --coverageReporters=json-summary
• lines: 94.61%
• test suites: 20 passed

[coveralls]

Pull Request Test Coverage Report for Build 23861677723

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+34.2%) to 90.741%

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Totals
Change from base Build 23857345948:	34.2%
Covered Lines:	457
Relevant Lines:	483

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💛 - Coveralls