[Skills& VA] Fallback rule support

[DingmaomaoBJTU]

Purpose

[Part 2] Close #1598 Remove "do you want to hear more" type prompts from Skills

Changes

1. Add fallback event send & handle in Email/Calendar skill, tested
2. Add fallback event redispatch handle logic in VA

Tests

Menual tested all possible senarios.

Feature Plan

Are there any remaining steps or dependencies before this issue can be fully resolved? If so, describe and link to any relevant pull requests or issues.

Checklist

General

• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the appropriate tests
• I have updated related documentation

Bots

• I have validated that new and updated responses use appropriate Speak and InputHint properties to ensure a high-quality speech-first experience
• I have replicated language model changes across the English, French, Italian, German, Spanish, and Chinese .lu files and validated that deployment is successful

Deployment Scripts

• I have replicated my changes in the Virtual Assistant Template and Sample projects
• I have replicated my changes in the Skill Template and Sample projects