feat: Add DSA solutions for beginner, intermediate, and advanced issues

[Santosh-Ku-Sahoo]

Implemented solutions for the following issues from ISSUES_LIST.md:

Beginner:

• Add Palindrome Check solution | Any language | Strings | #2 Reverse String (3 approaches: slicing, two-pointer, recursive)
• Add Fibonacci (iterative) solution | Any language | Loops | #3 Palindrome Check (3 approaches with case/punctuation handling)
• Add Linear Search solution | Any language | Arrays | #4 Fibonacci (iterative + memoized recursive)
• Add Bubble Sort solution | Any language | Sorting | #5 Linear Search (first-occurrence + all-occurrences)
• Add Count Vowels in a String solution | Any language | Strings | #6 Bubble Sort (optimized with early termination)
• Add Find Max/Min in Array solution | Any language | Arrays | #7 Count Vowels
• Write a "Git Basics" guide for beginners | Writing, Git knowledge | #8 Find Max/Min in Array (single pass)

Intermediate:

• Add Merge Sort solution | Any language | Sorting, Recursion | #13 Binary Search (iterative + recursive)
• Add Linked List implementation | Python / C++ | Data Structures | #14 Merge Sort (divide and conquer)
• Add Valid Parentheses solution | Any language | Stack | #15 Linked List (full implementation with 7+ operations)
• Add BFS / DFS on a Graph | Python / JS | Graphs | #16 Valid Parentheses (stack-based)
• Add Longest Common Subsequence | Any language | DP | #17 BFS/DFS on Graph (adjacency list)
• Build a To-Do list app (HTML/CSS/JS) | HTML, CSS, JS | #18 Longest Common Subsequence (DP)

Advanced:

• Add LRU Cache implementation | Python / Java | #25 Dijkstra's Algorithm (priority queue)
• Build a Full React mini-project with state management | React, Redux | #26 LRU Cache (OrderedDict)

All files follow the two_sum.py style with header comments, docstrings, and comprehensive test cases.

🔗 Related Issue

Closes #

---

📝 What did you do?

---

🗂️ Type of Change

• ✨ New solution / feature
• 🐛 Bug fix
• 📝 Documentation update
• 🧹 Code cleanup / refactor

---

✅ Self-Review Checklist

• My code runs without errors
• I followed the folder structure from the README
• I added comments/docstrings explaining my logic
• My branch name is descriptive
• I linked the issue above
• I haven't modified unrelated files

---

📸 Screenshots / Output (if applicable)

---

💬 Anything else?