fix: use compose file directory for compose builds

[MestreY0d4-Uninter]

Changes

• Use the compose file directory as the build-time project directory when a Docker Compose file lives in a subfolder.
• Keep root-level compose files on the existing deployment workdir behavior.
• Apply the same calculation to custom compose build commands unless the user already supplied a project directory.
• Add regression coverage for nested and root compose file locations.

Issues

• Fixes [Bug]: Docker Compose in subfolder does not find dockerfile in parent folder #9525
• Supersedes fix: use compose file directory for compose builds #9813, which was auto-closed by the repository quality gate before the description was shortened.

Category

• Bug fix
• Improvement
• New feature
• Adding new one click service
• Fixing or updating existing one click service

Preview

N/A; backend deployment command fix.

AI Assistance

• AI was NOT used to create this PR
• AI was used (please describe below)

If AI was used:

• Tools used: Hermes Agent/Codex for investigation, edit, and validation.
• How extensively: AI-assisted implementation with human-directed scope and local verification.

Testing

• Focused Pest regression for nested/root compose build commands passed.
• Full custom compose build command unit test file passed.
• Related compose start command unit test file passed.
• Pint dirty format check passed.
• PHP syntax checks passed for the changed PHP files.
• Docker Compose smoke confirmed that a nested compose file resolves parent build context from the compose directory, not the deployment root.
• Local Coolify dev stack was built and started successfully; health, login, dashboard, Horizon, and Mailpit responded.
• The focused and related compose tests also passed inside the running local dev container.

Contributor Agreement

Important

• I have read and understood the contributor guidelines. If I have failed to follow any guideline, I understand that this PR may be closed without review.
• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate.
• I have tested all the changes thoroughly with a local development instance of Coolify and I am confident that they will work as expected when a maintainer tests them.