## Summary
* **What is the goal of this PR?**
Add end-to-end integrity verification for downloaded font files by
including CRC32 checksums in the font manifest and validating downloaded
`.cpfont` files on device.
* **What changes are included?**
- `generate-font-manifest.py`: compute and include `crc32` for each
`.cpfont` asset in the generated `fonts.json` manifest.
- `FontDownloadActivity.h`: extend manifest file metadata with `crc32`
and declare checksum helper.
- `FontDownloadActivity.cpp`: parse `crc32` from manifest, compute CRC32
of downloaded files using `esp_rom_crc32_le`.
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? _**YES**_
WuTofu
3efc863038