Fix PHPUnit dependency mount lifecycle

[chubes4]

Summary

Encode PHPUnit dependency mount paths with real newlines so managed post-install loading receives each plugin directory.

What changed

• Replaces the literal backslash-n separator with a real newline in generated PHPUnit PHP.
• Extends unit and real Playground integration coverage to multiple inactive dependency mounts, including the component under test.

How to test

1. Run npm run build; expect Workspace build completes successfully..
2. Run npx tsx tests/phpunit-project-autoload.test.ts; expect Generated PHP contains newline-delimited dependency mounts..
3. Run npm run test:playground-phpunit-readonly-cache-integration; expect Real Playground managed PHPUnit lifecycle passes..

Compatibility

Restores the documented inactive extra_plugins plus dependencyMounts contract from #1868. Single-mount callers remain unchanged; multi-mount callers now load every declared plugin as intended.

Evidence

• Base unchanged since verification: main remains at c751155.
• CI expected: WP Codebox CI after push
• Reviewer-resolvable source evidence: PHPUnit dependency mounts do not activate after database install #1881
• Reviewer-resolvable source evidence: Load component during Codebox PHPUnit lifecycle Extra-Chill/homeboy-extensions#2302
• Verified finalization base: main at c751155
• build: Passed
• downstream-canary: Passed
• phpunit-project-autoload: Passed
• playground-integration: Passed

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode via Homeboy
• Model: openai/gpt-5.6-sol
• Used for: Traced the generated PHPUnit lifecycle, fixed dependency mount encoding, added regression coverage, and verified the downstream real-runtime canary; Chris reviews and owns the change.

Source relationships

• Closes PHPUnit dependency mounts do not activate after database install #1881