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.

packages/opencode/tsconfig.json

@@ -12,13 +12,6 @@
       "@/*": ["./src/*"],
       "@tui/*": ["./src/cli/cmd/tui/*"],
       "@test/*": ["./test/*"]
-    },
-    "plugins": [
-      {
-        "name": "@effect/language-service",
-        "transform": "@effect/language-service/transform",
-        "namespaceImportPackages": ["effect", "@effect/*"]
-      }
-    ]
+    }
   }
 }