Fix image URLs in latest journal entry to use GitHub-hosted paths

[Copilot]

Latest journal entry used relative file paths for images, which only render locally but fail on GitHub.

Changes

• Updated image references in journal.md from relative paths to GitHub raw URLs
• Added HOW_TO_ADD_IMAGES.md documenting three methods for adding images to journal entries

Example

Before:

![alt text](image-1.png)
![alt text](image.png)

After:

![alt text](https://github.com/n1t5ua5/code-journal/raw/main/image-1.png)
![alt text](https://github.com/n1t5ua5/code-journal/raw/main/image.png)

Images now render correctly when viewed on GitHub, consistent with other journal entries that use full URLs.

Original prompt

i need the images inside the latest entry to be input into the file the same way the other images have been. how do i get the right url?

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