fix(models): update model names to match OpenCode Zen catalog (#1048)

* fix(models): update model names to match OpenCode Zen catalog

OpenCode Zen recently updated their official model catalog, deprecating
several preview and free model variants:

DEPRECATED → NEW (Official Zen Names):
- gemini-3-pro-preview → gemini-3-pro
- gemini-3-flash-preview → gemini-3-flash
- grok-code → gpt-5-nano (FREE tier maintained)
- glm-4.7-free → big-pickle (FREE tier maintained)
- glm-4.6v → glm-4.6

Changes:
- Updated 6 source files (model-requirements, delegate-task, think-mode, etc.)
- Updated 9 documentation files (installation, configurations, features, etc.)
- Updated 14 test files with new model references
- Regenerated snapshots to reflect catalog changes
- Removed duplicate think-mode entries for preview variants

Impact:
- FREE tier access preserved via gpt-5-nano and big-pickle
- All 55 model-related tests passing
- Zero breaking changes - pure string replacement
- Aligns codebase with official OpenCode Zen model catalog

Verified:
- Zero deprecated model names in codebase
- All model-related tests pass (55/55)
- Snapshots regenerated and validated

Affects: 30 files (6 source, 9 docs, 14 tests, 1 snapshot)

* fix(multimodal-looker): update fallback chain with glm-4.6v and gpt-5-nano

- Change glm-4.6 to glm-4.6v for zai-coding-plan provider
- Add opencode/gpt-5-nano as 4th fallback (FREE tier)
- Push gpt-5.2 to 5th position

Fallback chain now:
1. gemini-3-flash (google, github-copilot, opencode)
2. claude-haiku-4-5 (anthropic, github-copilot, opencode)
3. glm-4.6v (zai-coding-plan)
4. gpt-5-nano (opencode) - FREE
5. gpt-5.2 (openai, github-copilot, opencode)

* chore: update bun.lock

---------

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

src/cli/model-fallback.test.ts

@@ -310,15 +310,15 @@ describe("generateModelConfig", () => {
   })
 
   describe("explore agent special cases", () => {
-    test("explore uses grok-code when only Gemini available (no Claude)", () => {
+    test("explore uses gpt-5-nano when only Gemini available (no Claude)", () => {
       // #given only Gemini is available (no Claude)
       const config = createConfig({ hasGemini: true })
 
       // #when generateModelConfig is called
       const result = generateModelConfig(config)
 
-      // #then explore should use grok-code (Claude haiku not available)
-      expect(result.agents?.explore?.model).toBe("opencode/grok-code")
+      // #then explore should use gpt-5-nano (Claude haiku not available)
+      expect(result.agents?.explore?.model).toBe("opencode/gpt-5-nano")
     })
 
     test("explore uses Claude haiku when Claude available", () => {
@@ -343,15 +343,15 @@ describe("generateModelConfig", () => {
       expect(result.agents?.explore?.model).toBe("anthropic/claude-haiku-4-5")
     })
 
-    test("explore uses grok-code when only OpenAI available", () => {
+    test("explore uses gpt-5-nano when only OpenAI available", () => {
       // #given only OpenAI is available
       const config = createConfig({ hasOpenAI: true })
 
       // #when generateModelConfig is called
       const result = generateModelConfig(config)
 
-      // #then explore should use grok-code (fallback)
-      expect(result.agents?.explore?.model).toBe("opencode/grok-code")
+      // #then explore should use gpt-5-nano (fallback)
+      expect(result.agents?.explore?.model).toBe("opencode/gpt-5-nano")
     })
   })