Guard terraform validate on successful init and propagate failures

[phorcys420]

Problem

scripts/terraform_validate.sh had two related issues in validate_terraform_directory:

1. terraform validate was run even when terraform init failed. validate requires modules to be installed by init first, so an init failure (e.g. a bad module source) produced a cascade of misleading Module not installed errors that hid the real cause.

2. popd masked the function's exit status. Because popd was the last statement in the function, it always returned 0. Real terraform validate failures were printed but never recorded in $status, so the script exited 0 despite failures — validation could not actually fail CI.

Fix

• Short-circuit on init failure with a clear terraform init failed error and skip validate, surfacing the real problem.
• Capture terraform validate's exit code and return it explicitly (after popd), so failures propagate to $status and the script exits non-zero.

Validation

• bash -n and shellcheck --severity=warning (the level CI enforces) are clean.
• Functionally tested three cases against the patched function:
  • valid dir → init + validate succeed → returns 0
  • bad module source → init fails → clear error, validate skipped → returns non-zero
  • init-clean but validate-time error → returns non-zero

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