feat: add Qwen International provider with regional endpoints (#8)

* feat: add Qwen International and US provider catalogs

* refactor: merge qwen-us into qwen-intl with regions support

* refactor: merge regional providers into single files with regions

Merge qwen-intl.toml into qwen.toml with [provider.regions] for
intl (Singapore) and us (Virginia) endpoints.

Merge minimax-cn.toml into minimax.toml with [provider.regions.china]
including separate api_key_env for China endpoint.

Uses new RegionConfig table format instead of simple string URLs.

providers/minimax.toml

@@ -1,13 +1,18 @@
-# MiniMax (International) — https://minimax.io
+# MiniMax — https://minimax.io
 # Models: 8
+# Regions: international (default), china (minimaxi.com)
 
 [provider]
 id = "minimax"
-display_name = "MiniMax (International)"
+display_name = "MiniMax"
 api_key_env = "MINIMAX_API_KEY"
 base_url = "https://api.minimax.io/v1"
 key_required = true
 
+[provider.regions.china]
+base_url = "https://api.minimaxi.com/v1"
+api_key_env = "MINIMAX_CN_API_KEY"
+
 [[models]]
 id = "MiniMax-M2.7"
 display_name = "MiniMax M2.7"