Graph nodes gain a name; nodes are objective facts (no learner/session references)

Schema: GraphNode + ExtractedProposition carry 'name' — a short 2-6 word
header, the rendering handle. Node theory made explicit: a node is an
objective world-facing fact; the learner's relationship to it lives
entirely in the event ledger (state labels are derived, never stored).
Extractor + auditor instructions enforce it — misconceptions state the
wrong idea itself as a claim, never 'the learner believes Y'. Legacy
ledger lines without a name derive one from the statement on read.
graph-view: labels use the name; the detail panel shows name as header
and statement as body.

src/core/graph.ts

@@ -160,6 +160,7 @@ export function mergeFindings(chatId: string, findings: SessionFindings, deps: G
 		} else {
 			const graphNode: GraphNode = {
 				id: newGraphNodeId(),
+				name: p.name,
 				statement: p.statement,
 				aliases: [...p.aliases],
 				kind: p.kind,