Enforce explicit return types and ban implicit `any` on functions

[bootcodes]

Problem

Functions across the codebase are missing explicit return types and in some cases use implicit or explicit any, which undermines TypeScript's type safety guarantees and makes refactoring risky.
Missing return types allow silent regressions - a function can change what it returns without a compile error at the call site

Solution

• Enable noImplicitAny in tsconfig.json
• Enable @typescript-eslint/explicit-function-return-type ESLint rule (or @typescript-eslint/explicit-module-boundary-types) to enforce return types on all exported and public functions
• Ban explicit any usage via @typescript-eslint/no-explicit-any
• Fix all existing violations

Alternatives

No response