feat: publish gate lists the staged state; a missing or unreachable remote stops before the commit (#159)

Files changed:
- CHANGES.md
- INSTALL.md
- VERSION
- instructions/publish-cycle.md
- instructions/setup-instance.md
- tools/CONTRACT.md
- tools/chemenu/commands/git_publish.py
- tools/chemenu/tests/test_git_publish.py

instructions/publish-cycle.md

@@ -47,6 +47,12 @@ consistent.
 
 - **Ten or more files changed?** `publish` exits 42. Show the user its output and stop; see
   [gates.md](gates.md).
+- **Remote unreachable or not configured?** `publish` ends with exit 1 before it commits:
+  nothing is staged, committed or pushed, and the message names the remote. Ask the user whether
+  to commit locally with `--no-push`, and run that only on their answer. Never push by hand
+  (AGENTS.md invariant 5): the next `publish` that reaches the remote sends the local commit
+  together with whatever is new. A local-only instance, which has no remote at all, passes
+  `--no-push` on every call ([setup-instance.md](setup-instance.md), step 4).
 - **Query or lint pass?** Neither auto-publishes. Run `publish` only if asked to.
 - **Nothing under `kb/` changed?** Skip steps 1 and 2; a change to `tools/` or `instructions/`
   does not affect the catalog.