docs(claude): update the default branch after a PR merges, before branching

The branch-creation rule only said to pull before `git checkout -b`. After a
merge the local default branch lacks the merged commits and the release tags,
and branching from origin/<default> instead makes that the new branch's
upstream. The rule now covers both and names the repository's own default
branch.

Refs: RSRMID-3119

Author: KaiSchwarz-cnic

CLAUDE.md

@@ -78,8 +78,11 @@ pnpm run test-demo                # demo App against OT&E — needs credentials
   `build` (build tooling), `chore`, `docs`, `test`, `refactor`.
 - **Breaking changes:** add `BREAKING CHANGE: <summary>` to the commit body after a blank
   line, and document the consumer upgrade path in the same change.
-- **Branch creation:** `git checkout master && git pull --ff-only` before `git checkout -b`
-  — never branch from a stale local default branch or another feature branch.
+- **Branch creation:** before creating a branch, and again after any PR merges,
+  run `git checkout master && git pull --ff-only` first — it brings in the
+  merged commits and their release tags. Never branch from a stale local
+  `master`, from `origin/master` (it becomes the new branch's upstream) or from
+  another feature branch.
 - **Branch naming:** prefix with the Jira issue ID — `RSRMID-1234-short-description`.
 - **Pull requests:** include the Jira issue link in the description; after opening, add the
   PR URL as a comment on the Jira issue.