v0.14.2 — harden $HOME displacement, FIFO hang, and quadratic config checks

Fixed

• stitch add ~ can no longer relocate $HOME. add now rejects the resolved home directory (and its ~/-spelled variants) before any filesystem mutation, with a clear usage error. Previously the adopt path moved $HOME and then failed an internal home-identity check whose rollback was provably unable to restore it, leaving the entire home stranded inside the repo.
• apply --force can no longer displace $HOME. A whole-directory store with target = "~" under --force previously renamed $HOME to $HOME.bak and replaced it with a repo symlink, reporting success. Direct apply and plan execution now refuse to back up and link the resolved home directory.
• apply no longer hangs on a FIFO config/state file. The snapshot loader opens with O_NONBLOCK, so a no-writer FIFO fails fast with the same non-regular-file error other commands already produce, instead of blocking forever on open(2).
• Link-collision and plan-source resolution are no longer quadratic. check_link_path_collisions, check_link_name_collisions, and same-store target-overlap validation now use index/trie-style ancestor lookups; plan construction resolves each store's link sources once. A 20,000-file patterns = ["**"] store now resolves in ~1.4s (was >120s).