fix(mongodb): harden backup info collection

[weicao]

Problem

MongoDB legacy backup-info collection masks failures from the MongoDB client,
timestamp conversion, and datasafed. It also accepts missing or malformed size
records, writes metadata directly to the final path, and lets datafile backup
continue after metadata generation fails.

Change

• select mongosh when available and retain the legacy mongo fallback;
• preserve producer return codes while keeping credentials quoted and out of
  diagnostics;
• require a non-empty timestamp and exactly one canonical
  TotalSize: <decimal> datasafed record;
• publish valid metadata through a sibling temporary file and guarded rename,
  preserving the previous destination on every failure;
• stop the datafile action before archive work when backup-info collection
  fails, retaining its existing action-trap status/message/marker mapping; and
• add a dual-shell contract suite for producer failures, empty and malformed
  values, duplicate records, JSON safety, atomic publication, cleanup, and the
  embedded action surface.

Evidence

• focused ShellSpec: Bash 3.2 13/0, Bash 5.3 13/0;
• full MongoDB ShellSpec: Bash 3.2 91/0, Bash 5.3 91/0;
• dual syntax checks and ShellCheck warning severity pass;
• Helm lint and default/custom helper-before-consumer renders pass;
• strict fsck, diff-check, and clean worktree pass;
• official datasafed v0.0.1-v0.2.4 and main format independently verified as
  TotalSize: %d;
• fresh independent design review: DESIGN_CLEAR / BLOCKER_LIST0; and
• fresh independent implementation review: APPROVE / BLOCKER_LIST0.

Boundaries

This PR contains static and container-local evidence only. It does not claim
Kubernetes runtime acceptance, package readiness, formal product N, merge,
deploy, or release readiness.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 232 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (8e745a4) to head (98a28bf).

Files with missing lines	Patch %	Lines
...godb/scripts-ut-spec/backup_info_collector_spec.sh	0.00%	232 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #3279    +/-   ##
======================================
  Coverage   0.00%   0.00%            
======================================
  Files        165     166     +1     
  Lines      25632   25864   +232     
======================================
- Misses     25632   25864   +232     

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