Resolve validation schema open issues

[Code-Hex]

This PR clears the current validation-schema issue backlog in one pass.

What changed:

• Updated Zod and Valibot dev dependencies to the latest published versions, while keeping the generated Zod code compatible with Zod v3 and v4.
• Fixed nullable/default handling, native enum imports, enum defaults, array defaults, enumPrefix: false, and isolated declaration problems.
• Added Zod options for nullable behavior, strict objects, descriptions, operation result schemas, enum-only output, and max-depth handling for cyclic object graphs.
• Expanded directive mapping so argument-less directives, functions, and object arguments work.
• Fixed Valibot lazy/nullish ordering and added Yup/MyZod regressions for enum defaults and Yup v1 array typing.
• Documented the client preset config shape and the new options.

Fixes #1414, #1362, #1361, #1342, #1275, #1271, #1270, #1262, #1251, #1187, #1119, #1086, #1039, #1026, #974, #781, #489, #472, #455, #422, #360, #359, #308.

Checked locally:

• pnpm exec tsc --noEmit
• pnpm test
• pnpm lint
• pnpm build