Add real-time Zoom transcript assistant starter tool

[KanikaGupta695]

Summary

• add a concrete Zoom webhook adapter (/zoom/webhook) with support for:
  • endpoint.url_validation challenge response
  • optional signature verification (x-zm-signature, x-zm-request-timestamp)
  • transcript extraction across common Zoom payload variants
• add websocket answer stream endpoint (/ws/answers) for live UI consumption
• add desktop overlay app (zoom-live-assistant-overlay) using Tkinter + websocket-client to display suggested answers instantly
• update configuration with ZOOM_WEBHOOK_SECRET and VERIFY_ZOOM_SIGNATURES
• add adapter unit tests and expand README usage examples for webhook + overlay setup

Why

This directly extends the tool toward production-like real-time usage: Zoom events can hit a single webhook endpoint, and generated answers are shown instantly in a lightweight desktop overlay.

Validation

• python3 -m pip install -e ".[dev]"
• python3 -m pytest (7 passed)