test(integration): scenarios 03/04 INPUT_MAX_RETRIES=3 masks #138 TLS-handshake flake without diagnosing root cause

## Problem

\`tests/integration/scenarios/03-ftps-explicit-upload.sh\` and \`04-ftps-implicit-upload.sh\` set \`INPUT_MAX_RETRIES=3\` (was 1 before #135). The bump was added as defense-in-depth against the Mode B TLS-handshake flake (#138), but it has the side effect that any lftp-vs-vsftpd regression that only fires on the first attempt is masked by the retry and never surfaces in CI.

## Impact

The scenarios no longer detect regressions that only manifest on the first connection attempt. The action's actual default (\`INPUT_MAX_RETRIES=10\`) is what users see in production, so the test's defence-in-depth doesn't even match production behaviour.

## Suggested Fix

Three options (any one):
- Restore \`INPUT_MAX_RETRIES=1\` and assert the scenario completes on the first attempt (closes #138 if Mode B doesn't re-emerge in 5 consecutive CI runs).
- Add an explicit assertion that the captured log contains \"Try #1\" succeeding, so a future Mode B re-emergence surfaces as a test failure with a clear diagnostic.
- Investigate the vsftpd-vs-lftp TLS handshake root cause (separate issue).

## Source

F2 audit (v2.11.2), explorer-scenarios-ftps (HIGH, relates to existing #138).