fix(mongodb): fail closed on uncertain member role

[weicao]

Problem

mongodb-member-leave.sh discarded the exit status from syncerctl getrole.
That made an uncertain role observation fail open: a timeout (124) or another
probe failure (7) with stale secondary output fell through to
syncerctl leave and returned success.

This conflicts with the addon lifecycle contract that member-leave actions
must repeat or fail safely and that diagnostic failures remain distinct from
successful convergence.

Change

• Capture role stdout and the original probe exit status separately.
• On a nonzero probe result, emit a bounded diagnostic, return the same status,
  and do not invoke leave.
• Preserve the existing exact primary rejection.
• Preserve KB_LEAVE_MEMBER_POD_NAME as the leave identity.
• Keep syncerctl leave as the terminal command so its exit status propagates.

Test-first evidence

Exact test-only parent 086e64d277761ee8d750e0d08e5775585d1ba91c:

• Bash 3.2.57: 4 examples, 2 failures
• Bash 5.3.9: 4 examples, 2 failures
• Exact failures: timeout 124 and probe rc 7 with stale secondary; both
  incorrectly returned 0 and invoked leave.

Exact implementation head 8f4da6594ef752a183eeb5226777c40c02cf757c:

• Focused spec, Bash 3.2.57 / 5.3.9: 5/0 each
• Full MongoDB specs, Bash 3.2.57 / 5.3.9: 83/0 each
• Dual Bash syntax, dual ShellSpec syntax, ShellCheck error-level, diff-check,
  strict fsck, ASCII, credential-shape, and clean-worktree gates pass.
• Fresh independent Dev review: APPROVE/BLOCKER_LIST0.

Review focus

• Role-probe exit-status boundary and stale-output behavior
• Exact member identity passed to leave
• Preservation of primary rejection and terminal leave status

This PR proves the repository source/test contract only. It does not claim
package, Kubernetes, controller, syncer runtime, deployment, release, or
accepted test-run results.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (8e745a4) to head (8f4da65).

Files with missing lines	Patch %	Lines
...db/scripts-ut-spec/member_leave_role_probe_spec.sh	0.00%	45 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3275   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        165     166    +1     
  Lines      25632   25677   +45     
=====================================
- Misses     25632   25677   +45     

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