fix(postgresql): fail invalid PITR recovery times

[weicao]

What

Validate and format the PostgreSQL PITR recovery timestamp before repository access or restore handoff mutation.

Why

The command substitution inside the recovery.conf heredoc masked date failures. An invalid timestamp could therefore return success, access the WAL repository, write an empty recovery target, and move DATA_DIR to .old.

Tests

• RED (76e2030e5): Bash 3.2 focused ShellSpec, 15 examples / 1 failure / 5 failed assertions
• GREEN: Bash 3.2 focused ShellSpec, 15 examples / 0 failures
• GREEN: Bash 5.3 full PostgreSQL ShellSpec, 283 examples / 0 failures
• ShellCheck error severity, Bash syntax, and git diff --check
• helm lint addons/postgresql: 1 chart / 0 failures
• helm template: 41 documents / 1,014,156 bytes

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (cb7ad58) to head (9fd582d).

Files with missing lines	Patch %	Lines
...ns/postgresql/scripts-ut-spec/pitr_restore_spec.sh	0.00%	12 Missing ⚠️

Additional details and impacted files

@@                           Coverage Diff                           @@
##           easton/pg-pitr-restore-start-wal-filter   #3400   +/-   ##
=======================================================================
  Coverage                                     0.00%   0.00%           
=======================================================================
  Files                                          195     195           
  Lines                                        28360   28372   +12     
=======================================================================
- Misses                                       28360   28372   +12     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.