fix(postgresql): stop failed PITR WAL pulls

[weicao]

Summary

• fail PITR restore immediately when datasafed pull cannot retrieve a required archived WAL
• stop before inspecting the missing destination or pulling later WALs across the resulting archive gap
• add focused ShellSpec coverage for the first-failure boundary

Contract anchors

• docs/addon-continuous-backup-pitr-chain-integrity-guide.md, pit 4: archive chains fail closed at missing segments
• docs/addon-api/09b-backup-extensions.md: restore must fail clearly when required repository artifacts are unavailable
• docs/addon-api/09c-restore-and-rebuild.md: PITR acceptance requires the continuous chain and post-restore result, not only a restore timestamp

TDD evidence

RED commit 87c2e128b (Bash 3.2): 9 examples, 1 failure / 3 failed assertions. A simulated rc44 pulling required WAL002 returned success, emitted no pull diagnostic, and continued to pull WAL003.

GREEN commit 7fe7358b05a2cc7d3e11300e089f06407cbeeee8:

• focused PITR restore ShellSpec on Bash 3.2: 9 examples, 0 failures
• full PostgreSQL ShellSpec on Bash 5.3: 277 examples, 0 failures
• ShellCheck error severity, Bash syntax, and diff check: clean
• Helm lint: 1 chart, 0 failures
• Helm render: 41 documents, 1,012,973 bytes

Scope

Source/static product change only. Runtime package, environment, execution, cleanup, and formal repeated-full acceptance remain tester-owned and are not claimed here.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (4dc19e2) to head (7fe7358).

Files with missing lines	Patch %	Lines
...ns/postgresql/scripts-ut-spec/pitr_restore_spec.sh	0.00%	10 Missing ⚠️

Additional details and impacted files

@@                        Coverage Diff                        @@
##           easton/pg-pitr-restore-list-order   #3394   +/-   ##
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  Coverage                               0.00%   0.00%           
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  Files                                    195     195           
  Lines                                  28303   28313   +10     
=================================================================
- Misses                                 28303   28313   +10     

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