Cost tiers: presets (Economy / Balanced / Performance)

[jcast90]

Why

Most users will not hand-tune a role→model table. Presets give a one-click cost posture; advanced users keep the per-role override.

Depends on

• Per-role model routing foundation (separate ticket)

Scope

Three presets that write the per-role model table:

Role	Economy	Balanced	Performance
chat	Haiku	Haiku	Sonnet
research	Haiku	Sonnet	Sonnet
plan	Sonnet	Opus	Opus
implement	Sonnet	Sonnet	Sonnet
review/debug	Sonnet	Sonnet	Opus

• Settings UI: preset selector + a "customize" affordance that exposes the role table
• Switching preset writes through to the role table (not a parallel concept)
• Default preset for new installs: Balanced

Out of scope

• Per-turn model override (separate ticket)
• Cost dashboard (separate ticket)