[WIP] feat: Category-based task routing

[quangdang46]

Gap #11 — High

Route tasks by semantic category instead of model name.

Source: oh-my-openagent

What's needed:

• Categories: visual-engineering -> Gemini, ultrabrain -> GPT-5.5, quick -> GPT-5.4 Mini
• Per-category model, fallback chain, temperature, prompt appends
• Category resolver: existence check -> model resolution -> fallback chain -> variant
• User-configurable categories

Reference: oh-my-openagent src/tools/delegate-task/category-resolver.ts