Improve private PPTX verification and reproducible releases

[MaxHu-xuan]

Summary

• Let receipt creators use a neutral logical PPTX name without exposing the source basename.
• Validate logical names consistently across macOS, Linux, and Windows, including reserved device names.
• Add deterministic, metadata-scrubbed source archives and fixed wheel timestamps for safer releases.
• Clarify the bilingual user guide, privacy boundary, examples, and troubleshooting.

Safety and privacy

• Tests and fixtures are synthetic and contain no secrets or personal data.
• The change does not weaken documented fail-closed or output-safety rules.
• New files are covered by the privacy audit and package manifest.
• Raw setuptools source archives are explicitly blocked from release; only canonicalized archives may be uploaded.

Verification

• 65 tests pass; 1 Windows-only comparison test is skipped as expected on macOS.
• Source privacy audit passes for 31 files with 0 findings.
• Privacy canary self-test passes.
• Wheel and canonical source archive install and smoke tests pass.
• Two clean builds are byte-for-byte reproducible.

GitHub Actions remains the final evidence for the Linux, macOS, Windows, and Python 3.11-3.14 matrix.