[Feature Request] Channel Interoperability & Internationalization: Seamless cross-region, cross-platform agent experience

## Is your feature request related to a problem?

Coze has separate deployments (coze.cn for China, coze.com for international) with significant interoperability gaps:

1. **Agents can't work across regions** — An agent built on coze.cn can't serve users on coze.com, and vice versa
2. **Lark (飞书) vs Feishu disconnect** — Lark (international) and Feishu (China) are the same product but agents can only integrate with one
3. **Timezone handling is inconsistent** — Calendar events, scheduled tasks, and timestamps don't properly handle cross-timezone users (e.g., a user in UTC+5 creating events for a team in UTC+8)
4. **Payment integration gaps** — International users can't use WeChat/Alipay; Chinese users can't use international payment methods
5. **Content delivery** — Knowledge bases, templates, and skills are siloed by region

## Describe the solution you'd like

### 1. Agent portability across regions
- Export/import agent configurations between coze.cn and coze.com
- Automatic adaptation of region-specific integrations (Lark↔Feishu, payment methods)
- Single agent definition that works in both environments

### 2. First-class timezone support
- User timezone setting in profile (not inferred from server)
- All time displays in user's local timezone
- Calendar/schedule operations explicitly handle timezone conversion
- Sub-agents inherit parent's timezone context

### 3. Unified channel integration
- Lark/Feishu treated as one channel with region-specific endpoints
- Email, Slack, Discord, WeChat as peer channels with consistent API
- Cross-channel message routing (e.g., email → Lark notification)

### 4. Internationalization framework
- Agent UI respects user's locale (language, date format, number format)
- Knowledge base content can be multilingual with auto-detection
- Template/skill marketplace available across regions

## Additional context

I work across coze.cn and Lark (international version), and the friction is significant. Every integration needs to be done twice, timezone issues cause missed schedules, and the dual-region setup feels like two separate platforms rather than one.

For enterprise users with global teams, this is a blocking issue.

**Priority**: P1 — Essential for enterprise adoption and international growth.

The issue names no files, tests, or entry points. Start by breaking the proposal into agent portability, timezone handling, channel integration, internationalization, and regional payments/content, then identify the relevant subsystems and their existing boundaries. It has no single completion criterion; a contributor would need a narrower, agreed scope before implementation.

Written by the indexing model from the issue text.