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

docs/guide/agent-model-matching.md

@@ -121,6 +121,7 @@ Principle-driven, explicit reasoning, deep technical capability. Best for agents
 | ----------------- | ----------------------------------------------------------------------------------------------- |
 | **GPT-5.3 Codex** | Deep coding powerhouse. Autonomous exploration. Required for Hephaestus.                        |
 | **GPT-5.4**       | High intelligence, strategic reasoning. Default for Oracle, Momus, and a key fallback for Prometheus / Atlas. Uses xhigh variant for Momus. |
+| **GPT-5.4 Mini**  | Fast + strong reasoning. Good for lightweight autonomous tasks. Default for quick category. |
 | **GPT-5-Nano**    | Ultra-cheap, fast. Good for simple utility tasks.                                               |
 
 ### Other Models
@@ -170,7 +171,7 @@ When agents delegate work, they don't pick a model name — they pick a **catego
 | `ultrabrain`         | Maximum reasoning needed   | GPT-5.4 → Gemini 3.1 Pro → Claude Opus → opencode-go/glm-5 |
 | `deep`               | Deep coding, complex logic | GPT-5.3 Codex → Claude Opus → Gemini 3.1 Pro |
 | `artistry`           | Creative, novel approaches | Gemini 3.1 Pro → Claude Opus → GPT-5.4       |
-| `quick`              | Simple, fast tasks         | Claude Haiku → Gemini Flash → opencode-go/minimax-m2.5 → GPT-5-Nano |
+| `quick`              | Simple, fast tasks         | GPT-5.4 Mini → Claude Haiku → Gemini Flash → opencode-go/minimax-m2.5 → GPT-5-Nano |
 | `unspecified-high`   | General complex work       | Claude Opus → GPT-5.4 → GLM 5 → K2P5 → opencode-go/glm-5 → Kimi K2.5 |
 | `unspecified-low`    | General standard work      | Claude Sonnet → GPT-5.3 Codex → opencode-go/kimi-k2.5 → Gemini Flash |
 | `writing`            | Text, docs, prose          | Gemini Flash → opencode-go/kimi-k2.5 → Claude Sonnet |