feat: letter upload attachments

[ehsunahmadi]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 52.94118% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.92%. Comparing base (4e8ceaa) to head (29e0af0).
⚠️ Report is 92 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/room/mod.rs	56.25%	7 Missing ⚠️
...rates/matrix-sdk-ui/src/timeline/controller/mod.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6572      +/-   ##
==========================================
- Coverage   89.94%   89.92%   -0.02%     
==========================================
  Files         381      381              
  Lines      105871   105888      +17     
  Branches   105871   105888      +17     
==========================================
- Hits        95228    95224       -4     
- Misses       6999     7021      +22     
+ Partials     3644     3643       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

---

_{Comparing p-num:letro/upload-thumbnail-hardening-2026-05-13 (29e0af0) with main (c253114)}