refactor(rundown): resolve rundown data from a scope context

The editor and cuesheet had three overlapping notions of which rundown
they were showing: loaded-only data hooks, a prop-drilled RundownSource,
and a selection store which read the loaded rundown out of the query
cache. Rendering two rundowns at once was not possible.

Introduce a rundown scope: a context carrying the rundown identity
(id, isLoaded and a selection store) which the utility hooks read from.
useRundown, useEntry and friends keep their signatures and call sites,
they simply resolve their rundown from the enclosing scope. The app
mounts a scope at the root which follows the loaded rundown, so runtime
views are unaffected; the editor and cuesheet mount an editable scope
which also binds entry actions to the same rundown.

- useEventSelection becomes a per-scope store factory, so panels hold
  independent cursors and the store is handed its rundown instead of
  reaching for the loaded one
- the cuesheet selection is generalised to useRundownSelection with a
  namespace, so each surface persists its own choice
- the clipboard records the rundown an entry was copied from, leaving
  room for pasting across rundowns
- removes useScopedRundown and the prop-drilled RundownSource

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011a5cbVjNC5XXF88b2PkUCa

apps/client/src/common/context/EditableRundownScopeProvider.tsx

@@ -0,0 +1,24 @@
+import { PropsWithChildren } from 'react';
+
+import { useScopedEntryActions } from '../hooks/useEntryAction';
+import { EntryActionsProvider } from './EntryActionsContext';
+import { RundownScopeProvider, useRundownScope, type RundownScopeProviderProps } from './RundownScopeContext';
+
+/**
+ * Rundown scope for subtrees which mutate entries.
+ * Actions are bound to the same rundown as the data, so the two cannot disagree.
+ */
+export function EditableRundownScopeProvider({ children, rundownId }: RundownScopeProviderProps) {
+  return (
+    <RundownScopeProvider rundownId={rundownId}>
+      <ScopedEntryActions>{children}</ScopedEntryActions>
+    </RundownScopeProvider>
+  );
+}
+
+function ScopedEntryActions({ children }: PropsWithChildren) {
+  const { rundownId } = useRundownScope();
+  const actions = useScopedEntryActions(rundownId);
+
+  return <EntryActionsProvider actions={actions}>{children}</EntryActionsProvider>;
+}