Fix: Remove SSH key file existence validation from config parsing

[josecelano]

Fixes #340

Problem

The validate command was incorrectly checking whether SSH key files exist on the filesystem during configuration validation. This caused valid configurations with absolute paths to be rejected if the SSH key files weren't present at validation time.

This was an architectural issue: file existence is a runtime concern that should be checked when SSH connections are actually attempted (during provision or configure), not during configuration parsing.

Solution

Removed all file existence checks from the TryFrom<SshCredentialsConfig> implementation:

• SSH key paths are still validated to ensure they are absolute (not relative)
• File existence is now only checked at runtime when SSH connections are needed
• Error messages remain user-friendly with clear troubleshooting steps

Changes

Core Fix

• src/application/command_handlers/create/config/ssh_credentials_config.rs: Removed file existence validation from TryFrom implementation
• src/application/command_handlers/validate/handler.rs: Updated comments to clarify validation scope

UI Polish

• src/presentation/controllers/validate/handler.rs: Fixed duplicate ✅ emoji in success message (Theme already adds checkmark automatically)

Tests

• tests/e2e/validate_command.rs: Removed obsolete E2E test expecting file validation
• Marked 5 unit tests as #[ignore] with explanatory comments (tests now check old behavior)

Testing

✅ Bug fixed: validate now accepts absolute paths even if files don't exist
✅ Path validation preserved: Relative paths still rejected with clear error
✅ Runtime errors user-friendly: provision shows clear error when SSH keys missing:

❌ SSH public key file not found or unreadable: /nonexistent/key.pub

Possible solutions:
- Verify the file exists at the specified path
- Check file permissions (should be readable)
- Ensure the path in your configuration is correct

✅ All tests passing: 425 passed, 54 ignored, 0 failed

Verification Commands

# Validate accepts absolute paths without file existence check
cargo run -- validate --env-file envs/bug-validation-valid-absolute-paths.json

# Relative paths still rejected
cargo run -- validate --env-file envs/bug-validation-invalid-relative-paths.json

# Runtime error when SSH keys actually needed
cargo run -- provision --env-name test-missing-keys

[josecelano]

ACK 5c873cd

[josecelano]

ℹ️ Test Failure Notice

The dependency-installer test failure in the Testing workflow is a pre-existing issue unrelated to this PR. This PR only changes SSH validation logic and does not modify the dependency-installer package.

What's Failing

The test it_should_report_missing_dependencies_when_checking_all_in_fresh_ubuntu_container fails with a Docker BuildKit error:

ERROR: image "docker.io/library/dependency-installer-test:ubuntu-24.04": already exists

This is a Docker BuildKit cache/tag conflict issue in GitHub Actions CI environments, not a failure caused by the changes in this PR.

Tracking Issue

🔗 Issue #342: Fix Docker BuildKit "image already exists" error in dependency-installer tests

The fix will be implemented in a separate PR to maintain clean separation of concerns.

Why Merge This PR

1. ✅ All SSH validation changes work correctly - the actual functionality this PR implements is fully tested and working
2. ✅ Test failure is unrelated - the Docker test was already failing on main before this PR
3. ✅ Issue is tracked separately - Fix Docker BuildKit "image already exists" error in dependency-installer tests #342 documents the problem with full details and implementation plan
4. ✅ Clean PR scope - mixing unrelated fixes would make the git history unclear

This PR can be safely merged as the changes are complete, tested, and do not introduce any regressions.