fix(prompt): open slash menu when typing / anywhere

[lucaslopesx]

Issue for this PR

Closes #16826

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The slash command menu only opened when / was typed as the first character in the prompt. Changed the slash detection to scan text before the cursor position instead of only checking if / is at index 0, allowing the menu to open anywhere in the prompt.

How did you verify your code works?

1. Open the prompt
2. Type hello
3. Type / the slash command menu now appears at the cursor

Screenshots / recordings

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential duplicate found:

• PR feat(app): support slash commands mid-prompt #16263: "feat(app): support slash commands mid-prompt" - feat(app): support slash commands mid-prompt #16263

  Why it's related: This PR appears to address the same underlying feature - enabling slash commands to work in the middle of prompts, not just at the start. The current PR (fix(prompt): open slash menu when typing / anywhere #16836) fixes the specific issue where the slash menu only opened when / was the first character, which aligns with the scope of allowing "slash commands mid-prompt."

I recommend checking PR #16263 to verify if it addresses the same issue or if the changes are complementary.