[no bump] Enable git hooks automatically on first bundle run

tools/bundle.py now sets `core.hooksPath scripts` the first time it runs in a
clone (skipped in CI, outside a git work tree, or when core.hooksPath is
already set), so the version auto-bump hooks work in fresh clones and repos
created from the template without a manual setup step. README documents the
hooks, the self-enabling behaviour and the bump stop words.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

scripts/post-commit

@@ -1,5 +1,6 @@
 #!/bin/sh
-# Companion to scripts/pre-commit.
+# Companion to scripts/pre-commit. Both are enabled per clone by tools/bundle.py
+# (it sets `core.hooksPath scripts` on its first run).
 #
 # `git commit -- <pathspec>` (also how some IDEs commit a file selection) builds
 # the commit from a temporary index. The pre-commit bump therefore lands in the