Feat(refactor): Migrate to Promises and declarative code for Concurrent Data Loading with Error Handling

[n-ce]

This PR completely refactors the application's data loading and rendering logic, moving away from verbose, imperative DOM manipulation toward a concise, high-performance, and declarative approach.

We replaced the sequential async/await pattern and element-by-element DOM construction with a single, efficient promise chain using Promise.all() and map/join.

Key Improvements

1. Performance and Concurrency

• Sequential $\rightarrow$ Concurrent: The application now uses Promise.all() to fetch both the /repos and /members endpoints simultaneously. The original method required waiting for the repositories to finish loading before starting the members fetch, resulting in unnecessary delays.
• Eliminated DOM Thrashing: The slow, many-step document.createElement and appendChild operations have been replaced by a single, fast innerHTML assignment. Array methods (map/join) build the entire HTML structure as a single string, drastically reducing rendering time.

2. Code Minimalism and Readability

• Maximized DRY Principle: We introduced a single, highly concise fetchData arrow function to handle URL construction and JSON parsing, eliminating repeated code.
• Unified Initialization: All necessary variables and the core fetch function are now declared on a single line using array destructuring, creating a minimal setup footprint.
• Reduced Boilerplate: Removed helper variables ($, x, reposUrl, membersUrl) and separate loading functions, executing the logic immediately within the promise chain.

3. Reliability

• Guaranteed Cleanup: Implemented .catch() and .finally() blocks to ensure robust error handling. The DOM is guaranteed to be updated (either with data or an error message), preventing silent failures and improving the user experience.