Fix setup script to update index.html title when using default value

[Copilot]

Problem

The setup script wasn't updating the title in index.html when users accepted the default presentation title by pressing Enter. This occurred because:

1. The default title was set to "Presentation Title" (line 40)
2. The placeholder text in index.html was also "Presentation Title" (line 7)
3. When sed tried to replace "Presentation Title" with "Presentation Title", no change occurred

As a result, users who accepted the default title ended up with a generic "Presentation Title" in their HTML instead of a meaningful title.

Solution

Changed the default presentation title from the static string "Presentation Title" to use the repository name ($REPO). Now when users press Enter to accept the default:

# Before
read -p "Enter presentation title [Presentation Title]: " TITLE
TITLE=${TITLE:-"Presentation Title"}

# After  
read -p "Enter presentation title [$REPO]: " TITLE
TITLE=${TITLE:-"$REPO"}

Examples

With git repository (e.g., my-awesome-talk):

• Press Enter → title becomes "my-awesome-talk"
• Enter custom text → title becomes the custom text

Without git repository:

• Press Enter → title becomes "YOUR-REPO-NAME" (still a placeholder, but gets replaced)
• Enter custom text → title becomes the custom text

This ensures the sed replacement always has an effect, properly updating both index.html and README.md with the chosen title.

Fixes #[issue-number]

Original prompt

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This section details on the original issue you should resolve

<issue_title>The script doesn't update the title in the index.html</issue_title>
<issue_description>The title in the index.html should be updated by the template fixup script.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #7

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