Fix portable launcher deps

[t3nka]

Summary

Fixes the portable launcher's dependency update action to use supported uv configuration and properly report failures.

Changes

• Replaces unsupported uv pip install CLI arguments with equivalent environment variables:
  • --timeout → UV_HTTP_TIMEOUT
  • --retries → UV_HTTP_RETRIES
  • --concurrent-downloads → UV_CONCURRENT_DOWNLOADS
• Preserves user-provided uv environment variable overrides
• Runs dependency install with check=True to catch failures
• Prevents checksum state from updating on install failure
• Shows error dialog to user on dependency update failure
• Adds focused tests for uv command formatting, environment handling, success path, and failure path

Testing

.\.venv\Scripts\python.exe -m pre_commit run --files app\ui\launcher\core.py app\ui\launcher\launcher_window.py tests\unit\ui\test_launcher_dependency_update.py
.\.venv\Scripts\python.exe -m pytest tests\unit\ui\test_launcher_dependency_update.py -q