Resolve the feeds.html conflict by keeping the branch's XSS-safe DOM
construction of the feed-details view and re-adding dev's per-feed and
reset-all error buttons via addEventListener instead of inline onclick,
since /feeds is a nonce-CSP page where inline handlers are blocked.
Update tests/test_feed_manager_extended.py::TestPollFeedPosting to patch
the SafeUrlPolicy.validate_async path (this branch's SSRF refactor) rather
than the removed module-level validate_external_url symbol, matching the
idiom already used throughout that test file.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>