feat: add Z.AI chat models + 5 new providers (#3)

* feat: add Z.AI chat models (GLM-5, GLM-4.7)

Sync with librefang/librefang#409 — add the two Z.AI chat models
to the standalone model catalog.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add 5 new providers (Stepfun, SiliconFlow, Baichuan, NVIDIA NIM, Writer)

- Stepfun (阶跃星辰): step-3.5-flash, step-3, step-2-mini, step-1o-turbo-vision
- SiliconFlow (硅基流动): inference platform, models discovered at runtime
- Baichuan (百川): Baichuan-4, Baichuan-3 Turbo 128K
- NVIDIA NIM: inference platform, models discovered at runtime
- Writer: Palmyra X5, X4, Med, Fin
- Add global aliases for stepfun, baichuan, writer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

aliases.toml

@@ -77,6 +77,13 @@
 "minimax-highspeed" = "MiniMax-M2.5-highspeed"
 "minimax-m2.1" = "MiniMax-M2.1"
 "codegeex" = "codegeex-4"
+"stepfun" = "step-3.5-flash"
+"baichuan" = "Baichuan4"
+"baichuan-4" = "Baichuan4"
+
+# Writer
+"palmyra" = "palmyra-x5"
+"writer" = "palmyra-x5"
 
 # ChatGPT Session Auth
 "chatgpt" = "gpt-5.1-codex-mini"