fix: support strict JSON Schema validators and resolve TypeScript compiler errors

[creatiVision]

Summary

This PR improves compatibility with strict JSON Schema validators (such as the Moonshot/Kimi API validator) and resolves a few strict TypeScript compiler errors in the codebase.

Changes

1. JSON Schema Compatibility:

   • Replaced z.tuple([z.number(), z.number()]) with z.array(z.number()).length(2) in src/mcp/tools/pdf-document.ts and src/mcp/tools/pdf-layout.ts.
   • Why: Standard JSON Schema Draft-07 represents Zod tuples as an array of schemas (items: [{type: number}, {type: number}]). Strict validators (such as Moonshot) reject array-based items schemas and require items to be a single schema object. Using z.array(z.number()).length(2) compiles to items: { type: 'number' }, minItems: 2, maxItems: 2 which is functionally equivalent but universally accepted by all JSON Schema engines.

2. TypeScript Fixes:

   • Resolved type narrowing errors in src/lib/yoga-resume/measure.ts and src/lib/yoga-resume/render.ts where element.bullets is optional and could be undefined.
   • Resolved pngBuffer possibly undefined error in src/mcp/tools/pdf-image.ts.