Harden Windows desktop launch and CI

[teloverge]

Summary

• package stellr-desktop.exe as the console-free Windows desktop entry while preserving stellr.exe as the interactive console CLI over shared application assembly
• harden Windows application and installer smokes with named deadlines, captured startup stages, real shortcut/protocol/display-icon assertions, and live PowerShell/cmd.exe CLI coverage
• upgrade all six artifact uploads to actions/upload-artifact@v7 without warning suppression

Validation

• cargo test --workspace --locked
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo fmt --all -- --check
• all PowerShell packaging contract suites
• 204 frontend tests, Svelte checks, and production frontend build via Vite+
• live release CLI smoke under native PowerShell and cmd.exe
• unsigned NSIS release build with direct PE assertions: desktop=WindowsGui, CLI=WindowsCui
• independent standards and spec reviews: no remaining actionable findings

Closes #75
Closes #76
Closes #77