fix(journal): re-init reactivity and drop var del

Make the reactivity engine re-initialize when the loaded declarations
change instead of only at import. ensureReactivity() reads the live
completions signal, compares a signature, and rebuilds from the store
(with exact bases) only when needed; dispatchCommand calls it before each
dispatch. Remove the unused DispatchContext.declarations/tagModifiers
fields, which were mount-time snapshots and could not be trusted.

Build initReactivity's maps into locals and commit only after the
circular check passes, so a failed re-init leaves the previous engine
intact; clear inFlight on commit.

Drop the unreachable var "del" action from the schema, render, and
reducer.

src/components/journal/index.ts

@@ -48,7 +48,7 @@ export { StreamMessageCard } from "./StreamMessage";
 export { ComposePanel } from "./ComposePanel";
 export { JournalInput } from "./JournalInput";
 export { DynamicForm } from "./DynamicForm";
-export { useJournalCompletions } from "./completions";
+export { useJournalCompletions, ensureReactivity } from "./completions";
 export { dispatchCommand } from "./command-dispatcher";
 export type { DispatchContext, DispatchResult } from "./command-dispatcher";
 export { parseInput } from "./command-parser";