Enable TypeScript strict mode across the codebase

[ivanvpetrov]

Summary

The project currently has no strict TypeScript compiler options set in tsconfig.json.
Enabling "strict": true will catch a class of bugs at compile time — null dereferences,
implicit any, missing type guards — and improve long-term maintainability.

##Proposed Change
Add "strict": true to the root tsconfig.json

{
  "compilerOptions": {
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true
  }
}

Then fix all uncovered errors