feat: initial product prototype (#1)

### Explanation

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### Issue

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### Attestations

- [x] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [x] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
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### Dependencies

- [x] I have pinned the dependencies to a specific patch version.

### Style

- [x] I have run the linter and resolved any errors.
- [x] My pull request uses an appropriate title, matching the conventional commit standards.
- [x] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
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### Versioning

Major - My pull request introduces a breaking change.

Reviewed-on: nhcarrigan/cordelia-taryne#1
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/utils/isSubscribed.ts

@@ -0,0 +1,40 @@
+/**
+ * @copyright nhcarrigan
+ * @license Naomi's Public License
+ * @author Naomi Carrigan
+ */
+import {
+  ActionRowBuilder,
+  ButtonBuilder,
+  ButtonStyle,
+  type ChatInputCommandInteraction,
+} from "discord.js";
+
+/**
+ * Checks if a user has an active entitlement (subscription) for the bot.
+ * If they do not, it responds to the interaction with a button to subscribe.
+ * @param interaction -- The interaction payload from Discord.
+ * @returns A boolean indicating whether the user is subscribed.
+ */
+export const isSubscribed = async(
+  interaction: ChatInputCommandInteraction,
+): Promise<boolean> => {
+  const isEntitled = interaction.entitlements.find((entitlement) => {
+    return entitlement.userId === interaction.user.id && entitlement.isActive();
+  });
+
+  if (!isEntitled && interaction.user.id !== "465650873650118659") {
+    const subscribeButton = new ButtonBuilder().
+      setStyle(ButtonStyle.Premium).
+      setSKUId("1338596712121499669");
+    const row = new ActionRowBuilder<ButtonBuilder>().addComponents(
+      subscribeButton,
+    );
+    await interaction.editReply({
+      components: [ row ],
+      content:    "You must be subscribed to use this feature.",
+    });
+    return false;
+  }
+  return true;
+};