feat(S3): visitor event types, VisitorsConfig, face_recognition dependency

Add KNOWN_VISITOR, UNKNOWN_VISITOR, VISITOR_DEPARTED to EventType enum.
Add VisitorsConfig model to config.py and wire into VigilarConfig.
Add face_recognition>=1.3.0 under [face] optional-dependencies in pyproject.toml.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -31,6 +31,9 @@ gpio = [
     "gpiozero>=2.0.1",
     "RPi.GPIO>=0.7.1",
 ]
+face = [
+    "face_recognition>=1.3.0",
+]
 dev = [
     "pytest>=8.2.0",
     "pytest-cov>=5.0.0",