chore: shared permission allowlist, screenshot script, gitignore

Add project .claude/settings.json (read-only cargo check/clippy + git diff
allowlist; personal settings.local.json stays gitignored). Add e2e/shots.mjs
(one-off mobile screenshot seeder). Ignore load-test run artifacts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -29,3 +29,6 @@ e2e/.env.test
 # OS
 .DS_Store
 Thumbs.db
+
+# Claude Code personal (per-user) settings — shared settings.json IS committed
+.claude/settings.local.json