Merge pull request #26 from KovaForge/minimax-backend

feat: add MiniMax as first-class chat backend

Adds skillopt/model/minimax_backend.py (clean port of qwen_backend.py
targeting MiniMax-M2.7 via https://api.minimax.io/v1) and registers it
in the router, backend_config, and common defaults. Existing backends
(openai_chat, claude_chat, qwen_chat, codex_exec, claude_code_exec)
remain bit-for-bit unchanged.

Verified via 10 import / routing / parity subtests; backward-compat
sweep across the 8 shipped configs passes with no regression.

A follow-up commit completes the YAML / CLI plumbing that this PR left
half-wired (FLATTEN_MAP entries, trainer-level configure_minimax_chat
call, and --minimax_* CLI args).

configs/_base_/default.yaml

@@ -44,6 +44,18 @@ model:
   target_azure_openai_ad_scope: "https://cognitiveservices.azure.com/.default"
   target_azure_openai_managed_identity_client_id: ""
 
+  # MiniMax backend settings (minimax_chat target)
+  minimax_base_url: ""          # https://api.minimax.io/v1 if blank
+  minimax_api_key: ""
+  minimax_model: "MiniMax-M2.7"
+  minimax_temperature: "0.7"
+  minimax_max_tokens: "8000"
+  minimax_enable_thinking: "false"
+  optimizer_minimax_base_url: ""    # per-role override
+  target_minimax_base_url: ""       # per-role override
+  optimizer_minimax_api_key: ""
+  target_minimax_api_key: ""
+
 train:
   num_epochs: 4
   train_size: 0          # 0 = derive from dataset split when available