Drop Following posts whose author blocked the viewer

[Pitchfork-and-Torch]

Bug

FollowingBlockedByHydrator asked socialgraph whether quoted_user_id or retweeted_user_id blocked the viewer. It never sent candidate.author_id. AuthorSocialgraphFilter then drops on author_blocks_viewer (unwrap_or false).

A native Following post from an author who blocked the viewer still served: author_blocks_viewer was written from retweeted_user_id only, so a non-retweet was Some(false). VFFilter None is fail-open, but this path is worse: it claims the author did not block the viewer.

Phoenix BlockedByHydrator already checks author_id. PR 100 added retweeted_user_id on For You. This is the Following twin of that missing native-author edge. This is not mute-on-retweet (PR 9) and not quote mute (PR 23).

Fix

Include author_id in check_blocked_by. Set author_blocks_viewer if either the primary author or the original retweeted author blocked the viewer. Keep quoted_author_blocks_viewer on quoted_user_id.

Proof

• Entry: FollowingBlockedByHydrator check_blocked_by on reverse-chron Following
• Sink: AuthorSocialgraphFilter author_blocks_viewer
• Break: Following never passed author_id into blocked-by
• Viewer effect: user blocked by A still sees A's native Following post (and A's retweet of B)
• Twin: Phoenix BlockedByHydrator author_id (PR 100 is the retweet original twin)

Tests

• native_author_who_blocked_viewer_is_marked (fails on unmodified main)
• retweet_of_author_who_blocked_viewer_is_still_marked
• retweeter_who_blocked_viewer_is_marked
• quoted_author_who_blocked_viewer_is_still_marked
• unit tests added; cargo test cannot run in the public dump (no Home Mixer Cargo.toml)