chore: expose pid + uptime on /health for crash-detection monitors

Adds `pid` and `uptime` fields to the /health response so external monitors
(and the local E2E watchdog) can detect a silent process restart between
two checks — e.g. an unhandled rejection that crashes Node and Docker
quietly relaunches the container.

Also adds .gitignore patterns for a local-only E2E suite that lives in
tests/e2e/local/ on individual machines and is never pushed.

.gitignore

@@ -100,6 +100,12 @@ backup/
 # Local artifacts from browser tooling
 .playwright-mcp/
 
+# Local-only E2E suite (never pushed; runs as pre-push gate on this machine)
+tests/e2e/local/
+playwright-local-results/
+e2e-test.log
+scripts/e2e-local.sh
+
 # Local SQLite files in backend
 backend/*.sqlite*
 backend/*.db