fix: use Alpine 3.24 to get ffmpeg 8.1.2 for correct HEIC transcoding

[SmilyOrg]

Problem

The Docker build produces corrupted/wrong thumbnails for HEIC files, showing blank/white areas instead of the actual image content.

Root Cause

Alpine 3.23 ships ffmpeg 8.0.1 which has a bug in HEIC tile assembly and orientation handling. When generating thumbnails from HEIC files:

• Only the first tile is output (2016×1512) instead of assembling all tiles
• The tile is incorrectly rotated 90° during scaling
• Produces a portrait image (183×256) instead of the correct landscape (256×192)

Fix

Upgrade to Alpine 3.24 which ships ffmpeg 8.1.2 — this fix resolves the HEIC tile assembly and orientation issues.

Verification

# Alpine 3.23 (broken):
ffmpeg -i IMG_3880.HEIC -vframes 1 -filter_complex "scale=..." -c:v pam ...
# → WIDTH 183, HEIGHT 256 (rotated, wrong)

# Alpine 3.24 (fixed):
# → WIDTH 256, HEIGHT 192 (correct)