feat: add portable signing runtime and desktop workflow

[guantw]

Summary

• Add a portable Windows runtime using a locked public OpenHarmony toolchain and Temurin Java runtime, so the packaged app does not require DevEco Studio, Python, Java, or HDC on the target machine.
• Add the desktop workflow, runtime/toolchain discovery, HAP signature inspection, cancellation and process cleanup, HDC lifecycle handling, diagnostics/settings, and secure token-cache handling.
• Add packaging scripts, provenance/license documents, third-party source attribution, and focused regression tests.

Validation

• python -m ruff check .
• python -m ruff format --check .
• python -m pytest --cov --cov-report=term-missing — 180 passed, 74.11% coverage
• git diff --check

Scope note

The locked portable toolchain currently covers the Windows release build. macOS/Linux runtime paths remain available for source/platform-specific builds but still require corresponding platform toolchain preparation and verification.