feat: keyword groups / presets (--preset ai-tools, --preset crypto)

[akvise]

Feature Request

Add built-in keyword presets so users can quickly analyze popular niches without typing keywords manually.

Usage:

trends-checker --preset ai-tools
trends-checker --preset crypto --geo US,EU
trends-checker --preset seo-tools --format json

Proposed presets:

Preset	Keywords
ai-tools	AI agents, vibe coding, cursor ide, llm, prompt engineering
crypto	bitcoin, ethereum, solana, defi, nft
seo-tools	ahrefs, semrush, moz, surfer seo, keyword research
web-frameworks	react, nextjs, svelte, vue, astro
saas	notion, linear, figma, vercel, supabase

Implementation:

• Define presets as a dict in cli.py
• --preset X sets kws before main loop (overridden by explicit --keywords)
• --list-presets flag to print all available presets

PRs welcome! See CONTRIBUTING.md.