Merge development into main: siGit Code 1.0.1

Promote the 1.0.1 release: GUI-launch PATH/ENOENT fix, model-cache EPERM fix, in-place tool-call streaming, ACP agent registry browser, VSIX packaging cleanup, and publish CI/CD for the VS Code Marketplace and Open VSX. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>