fix(etcd): resolve member actions through the current leader

[weicao]

What this changes

• execute etcd member join/leave on the Pod selected by the current leader role instead of relying on a Pod-creation-time LEADER_POD_FQDN
• verify the selected local endpoint is still the authoritative etcd leader before any membership mutation
• derive a bounded, canonical contact list from the action-time member list
• keep client TLS and peer TLS inputs separate
• preserve raw uint64 member-ID comparisons and reject malformed or ambiguous member ownership
• keep join/leave replay-safe with at most one membership mutation
• bound etcdctl calls to fit the lifecycle action deadline

Closes #3236.

Stacked delivery boundary

This PR is intentionally based on martin/etcd-memberjoin-idempotency, the exact head of #3235 (79c82e3ba6adb532625295a78046b82edd3a2d90). It contains only the follow-up commits through f130ae036bc999868a01d61a656c1c31c1682e3d.

Do not retarget Test from #3235 to this PR implicitly. This stacked PR starts with runtime N=0 and needs its own exact-head Test contract after the code/CI gate closes.

Verification

• genuine RED on the prior implementation for stale contact selection and canonical multi-owner ambiguity
• memberJoin focused: 65/0
• join + leave focused: 83/0
• full etcd ShellSpec: 116/0
• ambiguous pre-read: rc1, member-list-invalid, retry-safe no, mutation0, read1
• BusyBox production-function boundary: duplicate canonical owner rejected
• ShellCheck, Bash 3.2/5.3 syntax, diff-check, Helm lint/render: PASS
• independent B1 rereview: APPROVE/0 for exact f130ae036bc999868a01d61a656c1c31c1682e3d

The real-etcd matrix is N=1/version and supports only the bounded etcdctl timing claim; it does not execute the Kubernetes lifecycle action and is not a product Test or release verdict.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 483 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (79c82e3) to head (f130ae0).

Files with missing lines	Patch %	Lines
addons/etcd/scripts-ut-spec/member_join_spec.sh	0.00%	261 Missing ⚠️
addons/etcd/scripts-ut-spec/member_leave_spec.sh	0.00%	222 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##           martin/etcd-memberjoin-idempotency   #3237    +/-   ##
===================================================================
  Coverage                                0.00%   0.00%            
===================================================================
  Files                                     150     150            
  Lines                                   23843   24254   +411     
===================================================================
- Misses                                  23843   24254   +411     

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