fix(api): forward download request options

[KyleTryon]

Summary

• forward supported single-download options into task and yt-dlp kwargs
• support output templates, subtitle and thumbnail toggles, subtitle languages, cookie files, cookie headers, and browser-cookie extraction
• forward batch subtitle and thumbnail toggles through the existing batch task path
• add endpoint and task coverage for option propagation and template path handling

Validation

• uv run black app/api/v1/endpoints/downloads.py app/tasks/download_tasks.py tests/test_api/test_downloads.py tests/test_tasks/test_download_tasks.py
• uv run ruff check app/api/v1/endpoints/downloads.py app/tasks/download_tasks.py tests/test_api/test_downloads.py tests/test_tasks/test_download_tasks.py
• uv run pytest tests/test_api/test_downloads.py tests/test_tasks/test_download_tasks.py

[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 48.67%. Comparing base (1ec3045) to head (6395e62).
⚠️ Report is 49 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
packages/hermes-api/app/tasks/download_tasks.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #94      +/-   ##
==========================================
+ Coverage   40.59%   48.67%   +8.08%     
==========================================
  Files         145      139       -6     
  Lines        7119     6890     -229     
  Branches     1206     1075     -131     
==========================================
+ Hits         2890     3354     +464     
+ Misses       4222     3529     -693     
  Partials        7        7              

Flag	Coverage Δ		*Carryforward flag
backend	64.57% <96.42%> (+7.39%)	⬆️
frontend	31.12% <ø> (+6.78%)	⬆️	Carriedforward from ce85417

*This pull request uses carry forward flags. Click here to find out more.

Components	Coverage Δ
Frontend (hermes-app)	31.12% <71.71%> (+6.78%)	⬆️
Backend (hermes-api)	64.57% <91.17%> (+7.39%)	⬆️

Files with missing lines	Coverage Δ
...kages/hermes-api/app/api/v1/endpoints/downloads.py	57.40% <100.00%> (+23.67%)	⬆️
packages/hermes-api/app/tasks/download_tasks.py	80.18% <75.00%> (+68.16%)	⬆️

... and 11 files with indirect coverage changes