Adds PostProcessingExtractor — a zero-LLM keyword gate (Chinese +
English time words) followed by LLM extraction for ambiguous cases.
Events created from extraction carry source="post_extract" so the UI
can style them distinctly (R33). LLM gateway is optional to keep the
constructor testable without a live provider.
- src/agentkit/calendar/extraction.py — PostProcessingExtractor
- tests/unit/calendar/test_extraction.py — 13 tests with MockLLMGateway
chiguyong