v0.8.0 — Per-task cache invalidation and subprocess CWD anchoring

- New `--invalidate-cache [TASK]` flag: clears a single task's cache entry or the entire cache
- Subprocess CWD is now always anchored to the bam.yaml directory (fixes transient failures on parallel --no-cache runs)
- Local cache path and input globs resolved relative to bam.yaml (fixes cache misses on remote invocations)

See CHANGELOG.md for the full list of changes.