fix(err): propagate exit code from underlying command (#846)

[ousamabenyounes]

Problem

rtk err <cmd> and rtk test <cmd> always returned exit code 0, even when the underlying command failed. This broke CI/CD pipelines that rely on non-zero exit codes for error detection.

rtk err false # Output: [FAIL] Command failed (exit code: Some(1)) # Exit: 0 ← should be 1

Root Cause

run_err() and run_test() in src/cmds/rust/runner.rs computed exit_code but only passed it to tee_and_hint() — they never called std::process::exit().

Fix

Add std::process::exit(exit_code) after output when the child exits non-zero, matching the established pattern in git.rs, gt_cmd.rs, and all other command modules.

Tests

Two #[ignore] subprocess regression tests added:

• test_run_err_propagates_nonzero_exit_code — rtk err false → exits 1
• test_run_err_zero_exit_on_success — rtk err true → exits 0

cargo test cmds::rust::runner -- --include-ignored # 3 passed ✅ 

Fixes #846

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