refactor(gui): todos ride the generic projection pair; ConversationSnapshot evacuated

TodoDock reads useProjection('todos') (whole list or null pre-first-write;
absent renders nothing) and declare-merges the todos key through the pure-type
outlet — the identical member the tool-todo host unit owns, drift rejected by
any program holding both. The core Session's todos field, its todo/write case,
and the snapshot member retire; the client folds nothing. Session specs for
the retired client fold move to the value-store spec's seq coverage; snapshot
literals across component specs drop the field.

packages/client/ui-conversation/tsconfig.json

@@ -23,6 +23,9 @@
     {
       "path": "../runtime"
     },
+    {
+      "path": "../../session-projection/session-projection"
+    },
     {
       "path": "../ui-slash"
     },