v1.0.2 — cold-machine install fixes

Patch release — three more first-run fixes from real cold-machine installs (thanks again to our field tester 🙌). No feature changes.

Fixed

• Embedding model download failed on machines without a warm cache — even when explicitly authorized. semsearch set HF_HUB_OFFLINE/TRANSFORMERS_OFFLINE at import; huggingface_hub freezes those into module constants on first use, so the authorized download retry was a permanent no-op ("outgoing traffic has been disabled"). The offline-first guarantee now uses the local_files_only=True kwarg instead of env vars — same privacy promise, no frozen global state — and embed-sessions.py prints a 3-line actionable message instead of a 100-line traceback when the model is genuinely unreachable. New regression test runs against an empty HF_HOME.
• sb doctor could hang forever at the UI probe: the curl had no deadline, and a wedged/suspended process holding port 7655 accepts the TCP connect but never answers. The probe now has a 3-second timeout and distinguishes "UI not running" from "port held by a non-answering process — sb stop, then sb ui".
• sb ui on a busy port died with a bare exit 1. It now checks the port first and tells you the UI may already be running (and how to restart) instead of silently spawning a doomed process. Existing installs: re-run ./bin/install-cr.sh to pick up the new function.
• Post-install "what now?" moment: install.sh now ends with an unmissable next-steps block (./bin/install-cr.sh → source ~/.zshrc → sb ui / sb demo / sb doctor), matching bootstrap.sh — and mentioning the install-cr.sh step manual-clone users need before sb exists.

Full changelog: v1.0.1...v1.0.2