feat: migrate Provider.Model and Provider.Info to Effect Schema, add config providers HttpApi slice

- migrate Provider.Model from Zod to Schema.Class with Schema.mutableKey
  on fields that the provider service mutates (id, name, cost, options,
  headers, variants, api.id)
- migrate Provider.Info from Zod to Schema.Class with Schema.mutableKey
  on mutated fields (name, env, options, models)
- inner types (Mode, Interleaved, Capabilities, Cache, Cost, Limit, Api)
  stay as Schema.Struct to avoid adding named refs to the SDK
- derive .zod compat surfaces for existing Hono routes
- add config httpapi route with GET /config/providers using typed
  ConfigProvidersResponse schema
- wire into httpapi/server.ts and bridge /config/providers behind flag
- zero SDK diff confirmed