fix(llm): Tongyi-Qianwen embeddings use correct DashScope native API for intl URLs (#14784)

## Summary
- Fixes **Tongyi-Qianwen** (`QWenEmbed`) text embeddings when the
configured `base_url` points at DashScope **international**
(`dashscope-intl.aliyuncs.com`) or **China** (`dashscope.aliyuncs.com`)
hosts, including values copied from Model Studio that use the
**OpenAI-compatible** path (`.../compatible-mode/v1`).
- The `dashscope` Python SDK (`TextEmbedding.call`) expects the
**native** HTTP root (`https://<host>/api/v1`), not the
OpenAI-compatible base URL. Without mapping, international accounts
could hit the wrong host or path.

## Implementation
- Added `_dashscope_native_http_api_url()` to normalize known DashScope
hosts to `.../api/v1`, and wired `QWenEmbed` to set
`dashscope.base_http_api_url` before each embedding call (document and
query).

## Notes
- In-code comments document the Tongyi-Qianwen / DashScope intl vs CN
behavior for future maintainers.

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Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

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