Sync GSD — audit open-gsd/gsd-core for capabilities to absorb

tunan borrows capabilities from open-gsd/gsd-core but is not a fork of it. GSD is a separately-built TypeScript multi-runtime project; tunan re-expresses the borrowed idea in its own issue-state, skill-based shapes. So this skill is a capability audit, not a mechanical port:

• There is no path mapping and no branding transform (unlike sync-ups). A GSD file is never copied into tunan as-is.
• The unit of work is a capability, not a file. The question for each delta is "is there an idea here worth re-expressing in a tunan skill?" — answered by the maintainer, not auto-applied.

Load references/absorbed-capabilities.md at the start of every run — it records what tunan has already absorbed (so the audit does not re-surface it) and maps GSD's source tree to where capabilities live.

Phase 0: Preconditions