chore: gitignore .claude-flow scratch dirs

A claude-flow tool run left solitaire_engine/src/.claude-flow/. Ignore
.claude-flow/ anywhere in the tree, matching the existing agent-tooling
artifact rules.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -35,6 +35,8 @@ deploy/*-auth-secret.yaml
 /.agents/
 /.codex/
 /AGENTS.md
+# claude-flow scratch dirs, anywhere in the tree (e.g. solitaire_engine/src/)
+.claude-flow/
 
 # Local token-saving helper scripts (peek/cargoclip/testfail/diffclip/etc.) —
 # inspection-only Go tools, not committed. Tracked scripts/*.sh and *.md stay.