Add E2E tests to stop hook and README

- Stop hook now triggers on frontend/e2e/ changes
- Stop hook runs Playwright E2E tests alongside unit tests
- README documents test:e2e command and Playwright in code quality section

.claude/hooks/run-tests.sh

@@ -14,7 +14,7 @@ fi
 
 # Check for uncommitted changes in backend/frontend source
 HAS_BACKEND=$(git status --porcelain backend/src/ 2>/dev/null | head -1)
-HAS_FRONTEND=$(git status --porcelain frontend/src/ 2>/dev/null | head -1)
+HAS_FRONTEND=$(git status --porcelain frontend/src/ frontend/e2e/ 2>/dev/null | head -1)
 
 # Nothing changed -- skip
 if [[ -z "$HAS_BACKEND" && -z "$HAS_FRONTEND" ]]; then
@@ -38,9 +38,15 @@ fi
 # Run frontend tests if TS/Vue sources changed
 if [[ -n "$HAS_FRONTEND" ]]; then
     if OUTPUT=$(cd frontend && npm run test:unit -- --run 2>&1); then
-        PASSED+="✓ Frontend tests passed. "
+        PASSED+="✓ Frontend unit tests passed. "
     else
-        ERRORS+="Frontend tests failed:\n$OUTPUT\n\n"
+        ERRORS+="Frontend unit tests failed:\n$OUTPUT\n\n"
+    fi
+
+    if OUTPUT=$(cd frontend && npm run test:e2e 2>&1); then
+        PASSED+="✓ Frontend E2E tests passed. "
+    else
+        ERRORS+="Frontend E2E tests failed:\n$OUTPUT\n\n"
     fi
 fi