feat(categories): change quick category default model from claude-haiku-4-5 to gpt-5.4-mini

GPT-5.4-mini provides stronger reasoning at comparable speed and cost.
Haiku remains as the next fallback priority in the chain.

Changes:
- DEFAULT_CATEGORIES quick model: anthropic/claude-haiku-4-5 → openai/gpt-5.4-mini
- Fallback chain: gpt-5.4-mini → haiku → gemini-3-flash → minimax-m2.5 → gpt-5-nano
- OpenAI-only catalog: quick uses gpt-5.4-mini directly
- Think-mode: add gpt-5-4-mini and gpt-5-4-nano high variants
- Update all documentation references

src/cli/openai-only-model-catalog.test.ts

@@ -40,7 +40,7 @@ describe("generateModelConfig OpenAI-only model catalog", () => {
 
     // #then
     expect(result.categories?.artistry).toEqual({ model: "openai/gpt-5.4", variant: "xhigh" })
-    expect(result.categories?.quick).toEqual({ model: "openai/gpt-5.3-codex", variant: "low" })
+    expect(result.categories?.quick).toEqual({ model: "openai/gpt-5.4-mini" })
     expect(result.categories?.["visual-engineering"]).toEqual({ model: "openai/gpt-5.4", variant: "high" })
     expect(result.categories?.writing).toEqual({ model: "openai/gpt-5.4", variant: "medium" })
   })
@@ -55,6 +55,6 @@ describe("generateModelConfig OpenAI-only model catalog", () => {
     // #then
     expect(result.agents?.explore).toEqual({ model: "opencode-go/minimax-m2.5" })
     expect(result.agents?.librarian).toEqual({ model: "opencode-go/minimax-m2.5" })
-    expect(result.categories?.quick).toEqual({ model: "opencode-go/minimax-m2.5" })
+    expect(result.categories?.quick).toEqual({ model: "openai/gpt-5.4-mini" })
   })
 })