feat: add Xiaomi MiMo v2.5-pro and v2.5 model support (#14635)

## Merged

Adds MiMo v2.5-pro and v2.5 support to Xiaomi native provider, OpenCode Go, and setup wizard.

### Changes
- Context lengths: added v2.5-pro (1M) and v2.5 (1M), corrected existing MiMo entries to exact values (262144)
- Provider lists: xiaomi, opencode-go, setup wizard
- Vision: upgraded from mimo-v2-omni to mimo-v2.5 (omnimodal)
- Config description updated for XIAOMI_API_KEY
- Tests updated for new vision model preference

### Verification
- 4322 tests passed, 0 new regressions
- Live API tested on Xiaomi portal: basic, reasoning, tool calling, multi-tool, file ops, system prompt, vision — all pass
- Self-review found and fixed 2 issues (redundant vision check, stale HuggingFace context length)

agent/auxiliary_client.py

@@ -151,7 +151,7 @@ _API_KEY_PROVIDER_AUX_MODELS: Dict[str, str] = {
 # differs from their main chat model, map it here.  The vision auto-detect
 # "exotic provider" branch checks this before falling back to the main model.
 _PROVIDER_VISION_MODELS: Dict[str, str] = {
-    "xiaomi": "mimo-v2-omni",
+    "xiaomi": "mimo-v2.5",
     "zai": "glm-5v-turbo",
 }