fix: HEALTHCHECK detection respects dockerfile_target_build in multi-stage Dockerfiles

[jeongkichang]

Changes

When using multi-stage Dockerfiles with dockerfile_target_build, parseHealthcheckFromDockerfile searched the entire Dockerfile text for "HEALTHCHECK" regardless of target stage. This caused incorrect healthcheck configuration from other stages to be applied.

• Added extractTargetStageLines() to Application.php that parses FROM ... AS <stage> boundaries and returns only lines within the target stage
• When dockerfile_target_build is not set, falls back to original behavior (all lines)
• Added HEALTHCHECK NONE handling — returns early without applying any healthcheck config
• Added 6 unit tests for multi-stage HEALTHCHECK detection

Issues

• Fixes [Bug] HEALTHCHECK detection ignores dockerfile_target_build in multi-stage Dockerfiles #9475

Category

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

Preview

N/A — backend logic change, no UI changes.

AI Assistance

• AI was used (please describe below)

If AI was used:

• Tools used: Claude Code (code review, test generation)
• How extensively: AI assisted with test case generation and code review. Core logic was human-designed based on source code analysis.

Testing

./vendor/bin/pest tests/Unit/ApplicationHealthcheckMultiStageTest.php
# 6 passed (11 assertions)

./vendor/bin/pest tests/Unit/ApplicationHealthcheckRemovalTest.php
# 3 passed (7 assertions) — existing tests unaffected

Tested scenarios:

1. Target stage api with HEALTHCHECK → detected correctly
2. Target stage worker without HEALTHCHECK → not detected (fixed behavior)
3. No target stage set → falls back to all lines (backward compatible)
4. HEALTHCHECK NONE in target stage → treated as explicit disable
5. Case-insensitive stage name matching
6. Non-existent target stage → falls back to all lines

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.