[pengusto]

Summary

Nested OPML folders currently lose their descendant feeds. Import every descendant in document order into the existing outer group, preserving feed attributes and the flat group model.

 outer folder
   direct feed
-  nested folder → skipped
+  nested folder → visit its feeds and descendants

Addresses #1143 by retaining descendant feeds while preserving the existing flat group model.

Evidence

• Before: two new nested/default-group regressions fail; the official 0.16.2 APK imports 1/3 fixture feeds.
  After: all 13 app unit tests pass, including traversal order, empty folders and all three per-feed flags; an installed-APK backport imports 3/3.
• Validation: ./gradlew :app:testGithubDebugUnitTest on JBR 21 / Android SDK 36. No production settings or schema changes.
• APK captures are the official release payload versus its Penguin backport exported by Morphe Manager 2.2.0, not rebuilt current-main APKs. Raw fixture, XML, hashes and provenance.

Before	After

An optional selectable Penguin backport provides the same import behavior for the pinned official APK while this PR is reviewed; it is published in Penguin v1.4.0. AI-assisted implementation and test preparation; results above were executed locally.

Merge Danger

Door: two-way. Blast Radius: OPML imports.

Newly imported descendant feeds remain saved if code is reverted. Nested folders are flattened into their outer group; this does not introduce a nested-folder UI or database migration.