Update code-gpt article for W_o rollout and logits (no softmax)

[ahmadbasyouni10]

• File(s) Modified: articles/code-gpt.md
• Language(s) Used: python
• Submission URL: N/A (ML course solution article update, not a LeetCode submission)

Summary

Updates the Code GPT solution article to match the W_o output projection rollout and the softmax → logits change:

• Removes softmax from the solution — model now returns raw logits, not probabilities
• Adds output_proj = nn.Linear(model_dim, model_dim, bias=False) to the inner MultiHeadedSelfAttention class
• Updates all explanatory text from "probabilities" to "logits"
• Updates prerequisites to reference W^O instead of softmax
• Removes the softmax row from the shape walkthrough table
• Updates key takeaways to mention W^O

This is the companion to the neetcode.io PR that rolls out W_o to the Code GPT solution/starter code and updates the expected test output.