fix(multimodal-looker): update fallback chain order (#1050)

New order:
1. google/gemini-3-flash
2. openai/gpt-5.2
3. zai-coding-plan/glm-4.6v
4. anthropic/claude-haiku-4-5
5. opencode/gpt-5-nano (FREE, ultimate fallback)

Co-authored-by: justsisyphus <justsisyphus@users.noreply.github.com>

docs/guide/overview.md

@@ -112,9 +112,9 @@ Each agent has a **provider priority chain**. The system tries providers in orde
 
 ```
 Example: multimodal-looker
-google → anthropic → zai → openai → github-copilot → opencode
-   ↓         ↓         ↓        ↓           ↓            ↓
-gemini   haiku     glm-4.6  gpt-5.2    fallback     fallback
+google → openai → zai-coding-plan → anthropic → opencode
+   ↓        ↓           ↓              ↓           ↓
+gemini   gpt-5.2     glm-4.6v       haiku     gpt-5-nano
 ```
 
 If you have Gemini, it uses `google/gemini-3-flash`. No Gemini but have Claude? Uses `anthropic/claude-haiku-4-5`. And so on.
@@ -131,7 +131,7 @@ Here's a real-world config for a user with **Claude, OpenAI, Gemini, and Z.ai**
     "Atlas": { "model": "anthropic/claude-sonnet-4-5", "variant": "max" },
     "librarian": { "model": "zai-coding-plan/glm-4.7" },
     "explore": { "model": "opencode/gpt-5-nano" },
-    "multimodal-looker": { "model": "zai-coding-plan/glm-4.6" }
+    "multimodal-looker": { "model": "zai-coding-plan/glm-4.6v" }
   },
   "categories": {
     // Override categories for cost optimization