fix(postgresql): stop reconciliation at WAL gaps

[weicao]

Summary

• stop startup missing-WAL reconciliation at the first failed upload
• stop when a .done marker has no local WAL source
• prevent later WALs from being pushed across an unresolved repository gap

TDD evidence

• RED test commit: b9bea89d4 - 56 examples, 2 failures
• GREEN fix commit: 66953d5ad - focused 56 examples, 0 failures
• PostgreSQL ShellSpec with Bash 5: 269 examples, 0 failures
• ShellCheck severity error: clean
• Bash 5 syntax: clean
• git diff --check: clean
• helm lint addons/postgresql: 1 chart, 0 failures
• Helm render: 41 documents, 1,012,116 bytes

Behavior

Given ordered WALs 001 and 002, an upload failure or missing local source for 001 now returns immediately. WAL 002 is not pushed and backup metadata is not published until the gap is resolved.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (92e2da8) to head (66953d5).

Files with missing lines	Patch %	Lines
...ons/postgresql/scripts-ut-spec/pitr_backup_spec.sh	0.00%	24 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##           easton/pg-pitr-partition-validation   #3388   +/-   ##
===================================================================
  Coverage                                 0.00%   0.00%           
===================================================================
  Files                                      195     195           
  Lines                                    28215   28239   +24     
===================================================================
- Misses                                   28215   28239   +24     

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