Track non-hardware release roadmap

[tsotchke]

Summary

• add a software-improvement issue template for non-hardware work
• link the assistant roadmap and public launch plan to issues Build a denser binary term index for local recall #37-Prototype a C or assembly fixed-point kernel compatibility path #44
• include the new issue template in the preview-release package allow-list
• refresh the preview release manifest for the 706-file package

Verification

• .venv-torch311/bin/python -m unittest tests.test_build_preview_release tests.test_public_repo_hygiene tests.test_workspace_tracking
• .venv-torch311/bin/python scripts/build_preview_release.py --self-test
• git diff --check origin/main..HEAD

Physical hardware remains tracked separately in issues #1 and #2.