Handle expired invites & fix test registration (#73)

This PR addresses a bridge crash discovered while backfilling old channels, alongside a wee QoL fix for the test suite.

* **Expired Events (`d2m`):** Wraps Discord scheduled event/invite link lookups in a try-catch block. If a link is expired (404 or Discord error 10006), the bridge now posts a fallback `m.notice` rather than throwing an error and halting message conversion.
* **Test Suite Setup:** Updates `test.js` to initialize the mock registration object using `getTemplateRegistration()` preventing test runner crashes when running without a local `registration.yaml` file.

Co-authored-by: Cadence Ember <cadence@disroot.org>
Reviewed-on: https://gitdab.com/cadence/out-of-your-element/pulls/73
Co-authored-by: Bea <beanie@theargo.space>
Co-committed-by: Bea <beanie@theargo.space>

src/d2m/converters/message-to-event.test.js

@@ -1538,6 +1538,28 @@ test("message2event: vc invite event renders embed with room link", async t => {
 	])
 })
 
+test("message2event: expired/invalid invites are sent as-is", async t => {
+	const events = await messageToEvent({content: "https://discord.gg/placeholder?event=1381190945646710824"}, {}, {}, {
+		snow: {
+			invite: {
+				async getInvite() {
+					throw new Error(`{"message": "Unknown Invite", "code": 10006}`)
+				}
+			}
+		}
+	})
+	t.deepEqual(events, [
+		{
+			$type: "m.room.message",
+			body: "https://discord.gg/placeholder?event=1381190945646710824",
+			format: "org.matrix.custom.html",
+			formatted_body: "<a href=\"https://discord.gg/placeholder?event=1381190945646710824\">https://discord.gg/placeholder?event=1381190945646710824</a>",
+			"m.mentions": {},
+			msgtype: "m.text",
+		}
+	])
+})
+
 test("message2event: channel links are converted even inside lists (parser post-processer descends into list items)", async t => {
 	let called = 0
 	const events = await messageToEvent({