refactor(modifiers): remove double-casts in registry and schema

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/chess/src/modifiers/registry.ts

@@ -43,10 +43,10 @@ class ModifierRegistryClass {
           `Each modifier descriptor must have a unique id.`,
       );
     }
-    // Widen to the internal unknown-typed representation. The double-cast
-    // through `unknown` is intentional: the registry is a heterogeneous
-    // store and V is intentionally erased at storage time.
-    this.#byId.set(descriptor.id, descriptor as unknown as ModifierDescriptor);
+    // `ModifierDescriptor<V>` is not structurally assignable to
+    // `ModifierDescriptor<unknown>` due function-parameter variance.
+    // Erase V once at registry storage boundary.
+    this.#byId.set(descriptor.id, descriptor as ModifierDescriptor);
   }
 
   /**

packages/chess/src/modifiers/schema.ts

@@ -85,7 +85,7 @@ export const ModifierProfileSchema = z.object({
 
 /** Parse an unknown value as a ModifierProfile. Throws ZodError on failure. */
 export function parseModifierProfile(raw: unknown): ModifierProfile {
-  return ModifierProfileSchema.parse(raw) as unknown as ModifierProfile;
+  return ModifierProfileSchema.parse(raw) as ModifierProfile;
 }
 
 /** Serialize a ModifierProfile to a JSON-safe plain object. */