fix(sticker): send using the pack's image info instead of downloading the sticker

[eleboucher]

Description

Tapping a sticker did nothing. The send path downloaded and decoded the sticker purely to compute info, with no error handling, so any media failure meant sendEvent was never reached. It now uses the info the pack already declares, only measures the file when a pack omits it, and sends either way.

Fixes #1323

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

AI disclosure:

• Partially AI assisted (clarify which code was AI assisted and briefly explain what it does).
• Fully AI generated (explain what all the generated code does in moderate detail).