Preserve HEIC/HEIF transparency by converting to PNG

[qayshp]

Summary

• convert HEIC and HEIF attachments to PNG instead of JPEG while keeping TIFF on its existing JPEG path
• update converted paths, transfer names, MIME types, and logs to match the selected format
• route PNG conversion through a testable sips helper shared with the production file-system path
• add a repository-owned transparent HEIC fixture, a macOS-only alpha-preservation integration test, and a focused macOS CI workflow

Why

The attachment converter recognized HEIC, HEIF, and TIFF separately but sent every recognized image through a hard-coded JPEG path. That could discard alpha data in HEIC/HEIF images and made the resulting attachment metadata report JPEG unconditionally.

Behavior

HEIC and HEIF inputs now select PNG and image/png; TIFF continues to select JPEG and image/jpeg. Converted transfer names replace a matching source extension instead of accumulating extensions.

Validation

Validated on current head dc44e165 on SIP-enabled arm64 macOS:

• npm run test:image-conversion --workspace @bluebubbles/server — 5/5 tests passed
• the committed integration test converted the repository's transparent HEIC fixture through the production sips helper and verified PNG format with hasAlpha: yes
• targeted ESLint, Prettier, and git diff --check passed
• the workflow now targets the supported macos-15 image and current Node 24-based actions/checkout@v6 and actions/setup-node@v6, while installing the repository's required Node 20.11 runtime for the test

GitHub created an Image Conversion run for the current head, but it is action_required pending approval from an upstream maintainer because this is a fork pull request. No CI job has executed yet, so this is not presented as an observed CI pass.

The broader server type-check still reaches the pre-existing unrelated ScheduledService.ts:39 NodeJS.Timer/clearInterval error.

Fixes #787

[qayshp]

Self-review: the behavior and metadata paths are covered, with one integration-level follow-up noted inline.

[qayshp]

Validation update

Validated on SIP-enabled arm64 macOS 26.5.2 with Node 20.11.1 and npm 10.2.4.

• npm run test:image-conversion --workspace=@bluebubbles/server — 4/4 committed tests passed with the repository dependency tree available.
• A separate no-file-change smoke harness exercised the PR's actual convertImage() path with a repository-owned transparent image encoded as HEIC.
• The result existed as .png, reported image/png, used the expected .png transfer name, retained its 36×36 dimensions, and reported hasAlpha: yes before and after conversion.

The smoke harness was not added to the committed test suite. The review follow-up for a repository fixture and macOS CI integration test therefore remains open.

No messages were sent or received during validation. No screenshot is needed; format and alpha metadata provide stronger evidence for this change.

[qayshp]

Superseding the earlier workflow-status note: current head dc44e165 includes the repository-owned transparent HEIC fixture, the production-sips alpha-preservation test, and a focused workflow updated to the supported macos-15 runner with actions/checkout@v6 and actions/setup-node@v6. The focused suite re-passed 5/5 locally, including PNG output with hasAlpha: yes.

GitHub created the current-head workflow run, but it is action_required pending upstream maintainer approval for this fork PR. No CI job has executed, so an automated pass is not claimed.