Add sample guide, sample exports, and enriched build report

- examples/: sample guide store, .sfgz share archive, and exported
  output in all nine formats (JSON/MD/HTML×2/PDF/GIF/images/DOCX/PPTX)
- build_report.md now records packaging tool availability, fallback
  policy, offline guarantee, and verification entrypoints
- artifacts_manifest.json with sha256 checksums for packages + samples
- CHANGELOG entries for the welcome screen and renderer fixes

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

examples/sample-exports/image-bundle/reset-a-password-in-admin-portal-bundle.json

@@ -0,0 +1,30 @@
+{
+  "format": "stepforge-image-bundle",
+  "version": 1,
+  "guide": {
+    "title": "Reset a password in Admin Portal",
+    "generatedAt": "2026-06-11T02:32:07.575Z"
+  },
+  "steps": [
+    {
+      "number": "1",
+      "title": "Open Admin Portal users",
+      "image": "steps-reset-a-password-in-admin-portal/001-open-admin-portal-users.png"
+    },
+    {
+      "number": "2",
+      "title": "Enable the reset policy",
+      "image": "steps-reset-a-password-in-admin-portal/002-enable-the-reset-policy.png"
+    },
+    {
+      "number": "2.1",
+      "title": "Confirm permission prompt",
+      "image": null
+    },
+    {
+      "number": "3",
+      "title": "Review the confirmation",
+      "image": "steps-reset-a-password-in-admin-portal/004-review-the-confirmation.png"
+    }
+  ]
+}