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/layouts/BaseLayout.astro

@@ -9,7 +9,7 @@ interface Props {
 
 const {
   title,
-  description = "Community-driven collection of custom agents, prompts, and instructions for GitHub Copilot",
+  description = "Community-driven collection of custom agents, instructions, and skills for GitHub Copilot",
   activeNav = "",
 } = Astro.props;
 const base = import.meta.env.BASE_URL;
@@ -57,10 +57,6 @@ try {
               href={`${base}agents/`}
               class:list={[{ active: activeNav === "agents" }]}>Agents</a
             >
-            <a
-              href={`${base}prompts/`}
-              class:list={[{ active: activeNav === "prompts" }]}>Prompts</a
-            >
             <a
               href={`${base}instructions/`}
               class:list={[{ active: activeNav === "instructions" }]}