frontend: strict TypeScript & typed API models for cauweb

[ayushkrtiwari]

Goal

Tighten TypeScript to avoid runtime data shape issues and improve DX when consuming backend APIs.

Tasks

• Enable strict in tsconfig.json and fix resulting typing errors.
• Add generated types for API schemas (openapi/codegen or manual interfaces).
• Use zod/io-ts validators at boundaries to validate runtime data and return typed objects.
• Add CI step that runs tsc --noEmit to ensure type correctness.

Acceptance criteria

• npm run typecheck passes in CI and runtime schema mismatches are caught early.