fix(postgresql): traverse PITR history-only archives

[weicao]

What

Remove the directory-level latest-WAL shortcut and rely on sorted, exact per-object filtering during PITR archive traversal.

Why

A directory containing only required timeline-history metadata was skipped because the history basename sorted below the start WAL. Fetch returned success without downloading the metadata.

Tests

• RED dc172e1a1: Bash 3.2 focused, 19 examples / 1 failure / 2 assertions
• GREEN: Bash 3.2 focused 19/0; Bash 5.3 PostgreSQL full 287/0
• ShellCheck(error), syntax, diff clean; Helm lint 1/0; render 41 docs / 1,014,136 bytes

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (27005b6) to head (c79a640).

Files with missing lines	Patch %	Lines
...ns/postgresql/scripts-ut-spec/pitr_restore_spec.sh	0.00%	8 Missing ⚠️

Additional details and impacted files

@@                          Coverage Diff                           @@
##           easton/pg-pitr-restore-current-history   #3404   +/-   ##
======================================================================
  Coverage                                    0.00%   0.00%           
======================================================================
  Files                                         195     195           
  Lines                                       28397   28405    +8     
======================================================================
- Misses                                      28397   28405    +8     

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