feat(journey): convert HEIC/HEIF uploads to JPEG for cross-platform compatibility

HEIC is an Apple-only format not recognised as an image by many browsers
and platforms. heic-to (lazy-loaded) now converts HEIC/HEIF files to JPEG
before upload in both the gallery and entry editor photo pickers.
Embedded metadata (EXIF, GPS) may be lost during conversion — documented
in the Journey Journal wiki page.

wiki/Journey-Journal.md

@@ -37,6 +37,7 @@ Each entry corresponds to a day in your journey. The entry editor provides:
 
 - **Weather** — choose one of six values: Sunny, Partly cloudy, Cloudy, Rainy, Stormy, Cold.
 - **Photos** — attach photos to the entry. The first photo becomes the card thumbnail in list views.
+  > **Note on HEIC files:** HEIC is an Apple-only format that many browsers and platforms do not recognise as an image. To ensure broad compatibility, HEIC/HEIF files are automatically converted to JPEG before upload. This conversion may result in the loss of embedded metadata (EXIF data such as GPS coordinates, camera information, etc.).
 - **Pros / Cons** — optional verdict cards. Add items to a **Pros** list (thumbs-up) or a **Cons** list (thumbs-down) to summarise what you loved or what could have been better. These are stored in the `pros_cons.pros` and `pros_cons.cons` arrays on the entry.
 - **Tags** — free-form labels (e.g. "hidden gem", "best meal").
 - **Location** — pin the entry to a map location.