Copy TS webhook JSON fixtures and write parity tests

[patrick-chinchill]

Problem

Our integration tests use synthetic payloads that were hand-written to pass against the Python code — including its bugs. The TS repo has 28 recorded webhook JSON fixtures with real platform payloads.

Plan

1. Copy all 28 JSON fixtures to tests/fixtures/replay/
2. Write tests that replay each fixture through real adapters (not MockAdapter)
3. Assert output matches what TS produces for the same input
4. Add golden-output comparison for card rendering and emoji conversion

This is the #1 testing gap — it would have prevented most port bugs we found through manual review.