ci(config): 🎡 add multi-os build matrix, caching, release pruning and cleanup workflow

- expand build workflow to a matrix (windows, ubuntu, macos) and bump setup-python to v5
- add pip and PyInstaller cache steps and platform-aware PyInstaller invocation/staging
- produce OS-specific artifacts, archive per-OS, and adjust artifact naming/download patterns
- improve release job: use a dedicated short-SHA step, compute per-OS binary sizes, include file table in release notes, and toggle --latest/--prerelease based on a whitelisted branches env
- add a configurable "Prune Old Releases" step with daily-snapshot, max-count and dry-run support
- add a new cleanup workflow (cleanup.yml) to remove branch-associated releases on branch deletion or via manual dispatch, honoring protected branches and dry-run mode

Author: Mirrowel