The extractor's per-proposition understanding observations (named-word
scale: solid/shaky/accepted/...) were ledger data since the redesign,
with no surface. This exposes them at read time and shows each
session's note as a small chip on its session row in the node detail
card — the per-session confidence history the user asked for, one
observation per (node, chat), latest wins within a chat.
- GraphSnapshot.nodeObservations: nodeId -> chatId -> note, built in
graphSnapshot() from observation events (pure read-time join).
- Sessions list rows: link + observation chip.
- Session-relative judgments stay session-scoped: they render next to
their session, never as node state (the state model stays pending).