chore: track .claude/settings.json for the worktree base ref

`worktree.baseRef: head` is the setting CLAUDE.md's session workflow depends on:
without it EnterWorktree defaults to `fresh` and branches from `origin/main`,
which trails `develop` by ~75 commits. Shared config, so it belongs in the repo —
personal overrides still go in the ignored `.claude/settings.local.json`.

.claude/settings.json

@@ -0,0 +1,5 @@
+{
+  "worktree": {
+    "baseRef": "head"
+  }
+}