Reaction record

Purpose: Record one author adding tags to a thread (labels, likes, QDB votes) or a post (likes, flags) in one self-describing format. Scenario: A signed Like is saved as Target-Kind: thread in records/thread-labels/, beside its .asc signature. A legacy Thread-ID/Labels record from the same author for the same target and tag counts as the same vote. Thread scope drives labels and thread scores; post scope drives post scores and moderation. Legacy header sets are read only through a deprecated adapter so their support can be removed later. Sources: format, parser (source unavailable), legacy adapter (source unavailable), signed submission.