Add coverage thresholds to CI to prevent untested code from merging

[nanaf6203-bit]

Area: Testing Quality
Priority: P1 — High

Description

Tests might pass without actually exercising important code paths. Coverage thresholds in CI enforce a measurable floor on quality.

Acceptance Criteria

• Update package.json jest config with coverageThreshold:
  • branches: 80
  • functions: 85
  • lines: 85
  • statements: 85
• CI fails if any metric drops below threshold
• Coverage report uploaded to Codecov (or Coveralls) with token from secrets
• Coverage badge in README (shields.io or codecov.io)
• Exclude generated files, test files, DTOs, and entity definitions from coverage
• Document threshold rationale and exceptions in CONTRIBUTING.md

Technical Notes

• Use jest --coverage --coverageReporters=text-summary json lcov
• Codecov action: codecov/codecov-action@v4
• coveragePathIgnorePatterns: ['/node_modules/', '/dist/', '.*\\.dto\\.ts$', '.*\\.entity\\.ts$']

[awwalmust]

Hi maintainer
I have reviewed this issue and would love to work on it, PR 2days
Thanks

[grantfox-oss]

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