Add a beginner pwndbg challenge walkthrough

[codewithdaniel1]

Parent issue: #8

Create a practical walkthrough demonstrating how pwndbg is used to analyze a small vulnerable binary.

Scope

• Introduce the challenge binary
• Run the binary in pwndbg
• Trigger and inspect a crash
• Examine registers and the stack
• Generate a cyclic pattern
• Determine the overwrite offset
• Explain how pwndbg supports each analysis step
• Add the completed page to the MkDocs navigation

Acceptance criteria

• The walkthrough is reproducible
• The example is appropriate for beginners
• Required source code and compilation steps are included
• The documentation site builds successfully