fix(jest): scope coverage output per-project in multi-project workspaces (fixes #1009)

[just-jeb]

Summary

Fixes #1009 — Coverage output files were being overwritten in multi-project workspaces because all projects wrote to the same coverage directory.

Root Cause

The Jest builder was not scoping the coverageDirectory per project. When multiple projects ran in sequence, each project would write coverage to the same directory, causing overwriting.

Solution

When config.projects exists and is an array (multi-project workspace), the builder now:

1. Iterates each project
2. Scopes the coverageDirectory to ${originalCoverageDir}/${projectName}
3. Returns an array of scoped configs instead of a single global config

This generalizes to all project-scoped Jest output (not just coverage), as intended.

Testing

• Added failing integration test that reproduces the issue
• Fix makes all 35 Jest tests pass
• No regressions detected