core: remove @effect/language-service plugin and optimize hot path type performance

- Removed @effect/language-service from both packages/core and packages/opencode tsconfig files and dependencies

- Wrapped mergeDeep calls in config loading and LLM streaming to avoid expensive remeda conditional merge type instantiations in hot paths

- Narrowed Drizzle migrate() overload signature to avoid expensive variance checks during database initialization

These changes reduce TypeScript type-checking overhead and improve startup and runtime performance for config loading, LLM streaming, and database migrations.