v0.1.1

Fixed:
- Store::discover now honors the SYNTHESIST_DIR environment variable.
  Previously ignored, causing synthesist's --data-dir flag to silently
  fall through to parent-walk and init a fresh empty store at cwd when
  no claim ancestry existed. Worktrees and detached checkouts regressed.
- Explicit overrides that don't resolve to an existing store now fail
  loudly (missing path, not-a-directory, missing claims/genesis.amc).
  The silent auto-init on explicit paths is gone.