refactor(presets): split 'eu' into eu-eco/pro/max, drop xAI Grok

[Destynova2]

Summary

Refactors the eu preset (just merged in #296) into three sister presets with different cost/quality balances, and drops xAI Grok for sovereignty correctness.

Preset	Cost (4M tok/day, 22d)	Estimated SWE-V vs Opus 4.7 (87.6%)	Strategy
eu-eco	€15-25/month	~75-78%	Mid-size only — gpt-oss-120b default, Qwen3-Next-80B think, no 405B/397B heavyweights
eu-pro	€40-60/month	~82-85%	Balanced — Hermes-4-405B think, Qwen3.5-397B code, Qwen3-Next-80B-Thinking default
eu-max	€80-100/month	~85-87%	Preemptive — Qwen3.5-397B every default, Hermes-4-405B every think

Quality estimates are extrapolated from open-weight benchmark scores; this PR ships all three so users can grob preset apply <name> and benchmark them on real workloads. The --bench follow-up is intentionally a separate concern.

Why drop xAI Grok

The original eu.toml (#296) included xAI Grok via https://eu-west-1.api.x.ai/v1. After deeper research:

• xAI publishes a regional endpoint that fail-closes if EU cannot serve, but at-rest residency is unspecified in their public DPA (x.ai/legal/data-processing-addendum says "contact sales").
• No announced xAI EU datacenter — eu-west-1 is most likely partner-cloud (Memphis is xAI's only confirmed datacenter region).
• For users who genuinely need strict-EU sovereignty (the audience this preset family targets), this is a contract gap.

The unique benefit Grok provided was the 2M context window. Without it, max EU context drops to ~256k (Scaleway devstral-2-123b / Qwen3.5-397B-A17B). Sessions that exceed 256k normally trigger a Claude Code compact anyway, so the practical impact is minimal.

What changed

• presets/eu.toml → split into presets/eu-eco.toml, presets/eu-pro.toml, presets/eu-max.toml
• All three drop the xai_eu provider block and Grok model mappings
• Long-context tier (min_input_tokens > 150000) re-routes to Scaleway devstral-2 / Qwen3.5-397B (256k native) and Nebius Qwen3-235B (extensible 256k)
• presets/index.toml updated to list all three

Files

presets/eu.toml            (deleted, replaced by eu-pro.toml)
presets/eu-eco.toml        (new — cheap tier)
presets/eu-pro.toml        (renamed from eu.toml + xAI removed)
presets/eu-max.toml        (new — premium tier)
presets/index.toml         (updated)

Test plan

• grob preset info eu-eco / eu-pro / eu-max — all parse, providers/models/router slots wired
• No xAI/Grok references remain (grep -rE 'xai_eu|grok-' presets/eu-*.toml clean)
• No hardcoded version strings (CI guard)
• Docs lint passes in CI (markdownlint + lychee)

🤖 Generated with Claude Code