feat: add solution and tests for LeetCode Problem #1 - Two Sum

[SamehElalfi]

No description provided.

[Copilot]

Pull request overview

This PR adds a complete solution for LeetCode Problem #1 - Two Sum, implementing both an optimal hash map approach (O(n) time) and a brute force approach (O(n²) time) with comprehensive test coverage and documentation. The solution follows the repository's established patterns for organizing LeetCode problems.

Key Changes

• Implements two solution approaches with detailed complexity analysis and TSDoc comments
• Adds comprehensive test suite covering edge cases including negative numbers, zeros, large numbers, and duplicate values
• Updates problem statistics across repository documentation files

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
problems/1-two-sum/solution.ts	Implements hash map and brute force solutions with TSDoc comments and complexity annotations
problems/1-two-sum/solution.test.ts	Comprehensive test coverage for both solution approaches using Node.js test runner
problems/1-two-sum/README.md	Complete problem documentation with approach explanations, complexity analysis, and code quality checklist
problems/README.md	Updates problem index table and category sections, increments easy problem count from 1 to 2
README.md	Updates repository statistics from 1 to 2 total problems solved

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