Release v1.2.2: smoother conversion and clearer feedback

[ixiehao]

Summary

• Prepare v1.2.2 (build 8): timely progress reads, efficient conversion planning, and safer owned-process cancellation and output verification.
• Preserve display geometry/VFR across editing and merging; make media warnings conditional on actual loss and errors actionable in all three languages.
• Add regression coverage, concise trilingual changelog, and accurate privacy/distribution disclosures. Keep ad-hoc signing; no bundled FFmpeg or Developer ID requirement.

Validation

• swift test: 55 tests, 54 passed, one opt-in full-media benchmark skipped; no failures.
• Scripts/run-media-regression.sh: 28 checks passed.
• Localization and diff checks passed.
• Earlier authorized full-media queue benchmark and packaged-app GUI regression passed, including live progress, output decode, three languages, and failure recovery.
• Universal DMG will be rebuilt from this release source, verified, and uploaded with its SHA-256 after CI succeeds.

Runtime testing covers Apple silicon/macOS 27. Intel, minimum-OS hardware, and clean-account Gatekeeper behavior have not been re-tested. The release remains ad-hoc signed and unnotarized.