Surface wrangler error messages on command failure

[vliggio]

Summary

• When wrangler commands fail, the actual error from stderr is now logged prominently before the exception propagates
• Users will see the real wrangler error in the GitHub Actions step output instead of just a generic "process failed with exit code 1" message

Fixes #360

Test plan

• Run the action with a wrangler command that fails (e.g., deploy with invalid config) and verify the actual wrangler error appears in the step output
• Run the action with a successful wrangler command and verify behavior is unchanged