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/tools/AGENTS.md

@@ -95,7 +95,7 @@
 | ultrabrain | gpt-5.4 xhigh | Hard logic |
 | deep | gpt-5.3-codex medium | Autonomous problem-solving |
 | artistry | gemini-3.1-pro high | Creative approaches |
-| quick | claude-haiku-4-5 | Trivial tasks |
+| quick | gpt-5.4-mini | Trivial tasks |
 | unspecified-low | claude-sonnet-4-6 | Moderate effort |
 | unspecified-high | claude-opus-4-6 max | High effort |
 | writing | kimi-k2p5 | Documentation |