Remove prompts from website

Remove the prompts page, navigation link, homepage card, and all
references to prompts across the website source code. The repo no
longer contains prompt files, so the website should not reference them.

Files removed:
- website/src/pages/prompts.astro
- website/src/scripts/pages/prompts.ts

Files updated:
- BaseLayout.astro: remove nav link and update description
- index.astro: remove prompts card and update text
- llms.txt.ts: remove prompts import and section
- plugins.astro: update description text
- utils.ts: remove prompt type from install config, icons, labels
- pages/index.ts: remove prompts from counts
- modal.ts: update JSDoc comment

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/scripts/modal.ts

@@ -287,7 +287,7 @@ export function setupInstallDropdown(containerId: string): void {
 /**
  * Open file viewer modal
  * @param filePath - Path to the file
- * @param type - Resource type (agent, prompt, instruction, etc.)
+ * @param type - Resource type (agent, instruction, etc.)
  * @param updateUrl - Whether to update the URL hash (default: true)
  * @param trigger - The element that triggered the modal (for focus return)
  */