feat(minimax): Add full MiniMax M2.1 support

- Add MiniMax settings template (config/base-minimax.settings.json)
- Add MiniMax pricing (3 models: M2.1, M2.1-lightning, M2)
- Add validateMiniMaxKey() pre-flight validator
- Integrate MiniMax validation in main CLI flow
- Fix model name casing: M2.1-lightning (lowercase l)

Implementation follows GLM pattern:
- Anthropic-compatible API (no proxy needed)
- Pre-flight validation with health check
- Fail-open on network errors
- Actionable error messages

bun.lock

@@ -1,5 +1,6 @@
 {
   "lockfileVersion": 1,
+  "configVersion": 0,
   "workspaces": {
     "": {
       "name": "@kaitranntt/ccs",