fix: detect Live Photos before HEIC conversion

[DeveloperBlue]

For HEIC Live Photos, the server currently checks for the companion .mov file after conversion, incorrectly inside the Convert/ folder. This PR moves the check to before the conversion, so it correctly identifies the companion .mov next to the source HEIC image.

Summary

• Compute hasLivePhoto before convertImage / convertAudio rewrites filePath into Convert/.
• Companion .mov detection looks next to the original Messages path, so post-conversion checks always missed HEIC Live Photos.
• Once hasLivePhoto is true, the client requests and plays the correct image and .mov pair on its own, no additional work is needed.

Fixes #847

[DeveloperBlue]

I also have a two line client-side fix for clients that already have hasLivePhoto cached as false. Currently, resyncing on the app does not merge in the new attachment data; clients would have to clear their apps to see the live photo properly.

BlueBubblesApp/bluebubbles-app@master...DeveloperBlue:bluebubbles-app:developerblue/live-photo-sync

Let me know if it's worth PRing