feat(scenario): let context.downloadFile save data: URLs as run artifacts

Scenario steps can now persist in-script generated content (e.g. an
obtained VC's JWT) as a run file via context.downloadFile('data:...'),
without needing a network fetch. Bumps to 1.8.0.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "liqa",
-  "version": "1.7.1",
+  "version": "1.8.0",
   "private": true,
   "workspaces": [
     "server",