feat: ship VidXP application platform and desktop releases

[tulayha]

What changed

• completes the shared CLI, MCP, HTTP, browser, desktop, and container application platform
• adds the managed Tauri desktop runtime, system-tray lifecycle, private runtime/shared data layout, and native installer packaging
• publishes desktop artifacts and stable local/control/worker container images from release workflows
• restructures the product README around native CLI + MCP, desktop, and server/Coolify installation paths

Why

VidXP needs installable product surfaces that share the same runtime and data contracts, with release artifacts produced from the same validated commit instead of requiring users to assemble the product from the development repository.

Impact

• local users can choose CLI/MCP or a managed desktop installation
• desktop packaging owns its runtime and leaves shared models and repositories in the VidXP data root
• server operators can deploy immutable GHCR control and worker images with the documented Coolify Compose topology

Checks

• uv run pytest -q tests/test_packaging.py tests/test_settings.py (15 passed)
• cargo test --manifest-path desktop/src-tauri/Cargo.toml (7 passed)
• git diff --cached --check
• production Windows NSIS build and install smoke completed before this commit