Route cheap low-risk turns to economy

[mylukin]

Summary

• add a configurable cheap_model_low_risk classifier override for short current-turn read/check/status requests when the client explicitly asked for a cheap model
• scope the rule to the last user turn and block JSON, vision, code-changing, debug, deploy, security, math, and explicit heavy-model cases
• add schema coverage plus override and golden-routing regressions for the openclaw cost pattern

Verification

• corepack pnpm exec vitest run packages/core/src/classifier/overrides.test.ts packages/core/src/classifier/golden-routing.test.ts packages/shared/src/config/classifier-schema.test.ts
• corepack pnpm typecheck
• corepack pnpm lint (passes; existing info-level template-literal suggestion in packages/core/src/memory/forgetting/facts.test.ts)
• corepack pnpm build
• corepack pnpm test (322 files, 5008 tests)