feat: add NVIDIA NIM and MiniMax provider support (#552)

* feat: add NVIDIA NIM and MiniMax provider support

- Add nvidia-nim and minimax to --provider CLI flag
- Add model discovery for NVIDIA NIM (160+ models) and MiniMax
- Update /model picker to show provider-specific models
- Fix provider detection in startup banner
- Update .env.example with new provider options

Supported providers:
- NVIDIA NIM: https://integrate.api.nvidia.com/v1
- MiniMax: https://api.minimax.io/v1

* fix: resolve conflict in StartupScreen (keep NVIDIA/MiniMax + add Codex detection)

* fix: resolve providerProfile conflict (add imports from main, keep NVIDIA/MiniMax)

* fix: revert providerSecrets to match main (NVIDIA/MiniMax handled elsewhere)

* fix: add context window entries for NVIDIA NIM and new MiniMax models

* fix: use GLM-5 as NVIDIA NIM default and MiniMax-M2.5 for consistency

* fix: address remaining review items - add GLM/Kimi context entries, max output tokens, fix .env.example, revert to Nemotron default

* fix: filter NVIDIA NIM picker to chat/instruct models only, set provider-specific API keys from saved profiles

* chore: add more NVIDIA NIM context window entries for popular models

* fix: address remaining non-blocking items - fix base model, clear provider API keys on profile switch

src/services/api/openaiShim.ts

@@ -1360,8 +1360,12 @@ class OpenAIShimMessages {
       ...filterAnthropicHeaders(options?.headers),
     }
 
-    const isGemini = isEnvTruthy(process.env.CLAUDE_CODE_USE_GEMINI)
-    const apiKey = this.providerOverride?.apiKey ?? process.env.OPENAI_API_KEY ?? ''
+    const isGemini = isGeminiMode()
+    const isMiniMax = !!process.env.MINIMAX_API_KEY
+    const apiKey =
+      this.providerOverride?.apiKey ??
+      process.env.OPENAI_API_KEY ??
+      (isMiniMax ? process.env.MINIMAX_API_KEY : '')
     // Detect Azure endpoints by hostname (not raw URL) to prevent bypass via
     // path segments like https://evil.com/cognitiveservices.azure.com/
     let isAzure = false