practice fix follow-up — the picker lists EVERY birth-session group (owner ruling)

Owner escalation on deviation 1: practice availability must not
inherit a visual-rendering threshold. graphClusters() now runs
birthSessionPartition(snap.nodes) directly (same size-desc/id-asc
ordering) instead of reading the snapshot's MIN_CLUSTER_SIZE-filtered
clusters array — MIN_CLUSTER_SIZE stays a hull-drawing rule only.
Label join mirrors the snapshot's (chat title / notes path, null when
the naming record is gone). Contract doc + architecture.md sentence
corrected to match; empty-picker copy reworded ('once a session births
its first proposition' — no 3+ mechanics). Render pins: new empty line
+ a 1- and 2-proposition group listing pin. 1130/1130, tsc 0, lint 0,
build 0.

src/core/contracts/graph.ts

@@ -260,10 +260,11 @@ export interface Cluster {
 
 /** One birth-session cluster as the practice picker consumes it (owner
  *  ruling 2026-09-29: problem sets take NODES — the UI resolves a picked
- *  cluster to its member ids). Same grouping the graph view renders
- *  (birthSessionPartition semantics, MIN_CLUSTER_SIZE presentation
- *  filter included); `label` is null when the naming record is gone —
- *  honest, never guessed (the graph view renders those unlabeled). */
+ *  cluster to its member ids). EVERY birth-session group regardless of
+ *  size (owner ruling, same evening: MIN_CLUSTER_SIZE is a hull-drawing
+ *  rule — practice availability must not inherit a visual threshold);
+ *  `label` is null when the naming record is gone — honest, never
+ *  guessed (the graph view renders those unlabeled). */
 export interface GraphClusterGroup {
 	/** The birth session's id — a chatId or a notes source id. */
 	key: string;