docs(ops): document resilience and upgrade boundaries

[gfyrag]

Summary

• document multi-region topology trade-offs and the limits of remote learners
• make quorum-loss recovery explicit, including the leader-only force-remove boundary
• document scheduled backups, long-term retention semantics, and immutable restore points
• add the pre-GA server-binary upgrade decision tree and runbooks

Validation

• bash scripts/agent-check
• AI_REVIEW_BASE_SHA=6ca54e58cfdfa2e361e8b975e15e3afd66071a0e bash scripts/agent-check-pr

Both pass.

[NumaryBot]

✅ Approve — automated review

The documentation changes align with the current operator schema, CLI commands, Raft status fields, backup behavior, and force-removal implementation. No actionable correctness issues were found.

No findings.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.13%. Comparing base (6ca54e5) to head (e0a0a1e).

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v3.0    #1887      +/-   ##
================================================
- Coverage         77.16%   77.13%   -0.03%     
================================================
  Files               478      478              
  Lines             51258    51258              
================================================
- Hits              39552    39537      -15     
- Misses             8273     8290      +17     
+ Partials           3433     3431       -2     

Flag	Coverage Δ
e2e	77.13% <ø> (-0.03%)	⬇️
scenario	77.13% <ø> (-0.03%)	⬇️
unit	77.13% <ø> (-0.03%)	⬇️

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