ivnites: use actual inviteDTO for DOMInvite

no intermediary parsing step. Also, moved the date -> duration (3mo6d3h
sorta thing) to the web, there's now a ValidTill field with a unix
timestamp. Used the new Temporal api with a polyfill. Bumped api version
(although it still isn't semver).

package.json

@@ -38,6 +38,7 @@
     "remixicon": "^4.3.0",
     "remove-markdown": "^0.5.0",
     "tailwindcss": "^3.3.2",
+    "temporal-polyfill": "^0.3.0",
     "typescript": "^5.1.3",
     "uncss": "^0.17.3"
   },