feat(ui): add plugin command registry

docs/core-data-structures/core.md

@@ -19,6 +19,7 @@ Everything else is documented on a **sub-page**, not here. The rule that draws t
 | [token-meter.md](token-meter.md) | immutable scalar and positional replay measurements with consumed-log revisions |
 | [scope.md](scope.md) | scoped registration identity, dispatch carriers, and the owned `Scope` context |
 | [goal.md](goal.md) | persisted goal identity, lifecycle snapshots, activation, change records, and round attribution |
+| [commands.md](commands.md) | the human-command seam: definitions, surface discovery, direct invocation, results, and parsing views |
 | [session.md](session.md) | the full `SessionEventMap` variant catalog, `TurnTrigger`/`TurnEndReason`, `deriveMessages()`, the turn-enclosure invariant |
 | [persistence.md](persistence.md) | the durability seam: `SessionPersistence`, JSONL + SQLite backends, `session/flush`, crash recovery, `SessionHeader` |
 | [session-query.md](session-query.md) | logical records, bounded exact-event reads, and relationship traces |