Return actual user preferences instead of hardcoded values

Read posting:default:visibility, posting:default:sensitive, and
posting:default:language from the authenticated user's account
settings instead of returning hardcoded defaults from the
GET /api/v1/preferences endpoint.

Fixes #425

Author: vigneshakaviki

src/api/v1/index.ts

@@ -57,11 +57,17 @@ app.get(
   tokenRequired,
   scopeRequired(["read:accounts"]),
   (c) => {
+    const owner = c.get("token").accountOwner;
+    if (owner == null) {
+      return c.json(
+        { error: "This method requires an authenticated user" },
+        422,
+      );
+    }
     return c.json({
-      // TODO
-      "posting:default:visibility": "public",
-      "posting:default:sensitive": false,
-      "posting:default:language": null,
+      "posting:default:visibility": owner.visibility,
+      "posting:default:sensitive": owner.account.sensitive,
+      "posting:default:language": owner.language,
       "reading:expand:media": "default",
       "reading:expand:spoilers": false,
     });