Fix integration test script false failure

[brow]

What changed?

• Remove the nonexistent buzz-auth integration-test invocation that deterministically recorded a false failure.
• Let the workspace integration step expose real Cargo/test errors instead of suppressing stderr or using an unreachable fallback.
• Add a focused shell regression test and run it through the existing test-unit CI path.

Why?

run_test_step records failures but returns success, so the prior || ... true fallbacks were unreachable. Since buzz-auth has no integration-test target, every integration run recorded a phantom failure while hiding Cargo's explanation.

How is it tested?

• ./scripts/run-tests.sh unit passes (5 steps).
• Focused test-runner regression test passes directly and through just test-runner-script.
• Hermit-managed pre-push suites pass.
• Deep dual pre-review completed; its actionable finding to wire the regression test into CI was addressed.

Integration mode now has only the pre-existing, unrelated git-credential-nostr permission assertion failure. Its real diagnostics are visible on stderr, and the summary contains no buzz-auth integration tests failure.

Before / After

Images are impractical for this shell-script change; terminal output serves as the before/after evidence.

Before

exit=1
Failed (2):
  fail buzz-auth integration tests
  fail workspace integration tests

# The buzz-auth error was hidden by 2>/dev/null.
# Direct command:
error: no test target matches pattern `*` in `buzz-auth` package

After

integration_exit=1
Passed (1):
  pass buzz-db tests
Failed (1):
  fail workspace integration tests

thread 'missing_key' panicked ... expected exit 1 for missing key
thread 'bad_keyfile_permissions' panicked ... expected exit 1 for insecure keyfile permissions
[run-tests] workspace integration tests FAILED

# `buzz-auth integration tests` is absent.

Commit hook note

The global secret scanner flagged unchanged localhost development defaults at scripts/run-tests.sh:43 and .github/workflows/ci.yml:427 (postgres://buzz:buzz_dev@localhost:5432/buzz). Both strings already exist on main and match the repository's Docker Compose development configuration. After independent confirmation and explicit authorization in the BOT-1316 Buzz thread, this commit used the scanner's documented one-shot SKIP_SECRET_SCANNING=1 confirmation; every other commit hook remained active and passed. The diff introduces no credential-like strings.

🤖 This PR was authored with an agent (Buzz: BOT-1316 thread).

[brow]

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