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/stores/entryCopyStore.ts

@@ -2,13 +2,19 @@ import { create } from 'zustand';
 
 type EntryCopyStore = {
   entryCopyId: string | null;
+  /** rundown the copied entry belongs to, so a paste knows whether it crosses rundowns */
+  entryCopyRundownId: string | null;
   entryCopyMode: 'copy' | 'cut';
-  setEntryCopyId: (eventId: string | null, mode?: 'copy' | 'cut') => void;
+  setEntryCopyId: (eventId: string | null, rundownId: string | null, mode?: 'copy' | 'cut') => void;
 };
 
+/**
+ * The clipboard is shared across rundowns so entries can be moved between them
+ */
 export const useEntryCopy = create<EntryCopyStore>()((set) => ({
   entryCopyId: null,
+  entryCopyRundownId: null,
   entryCopyMode: 'copy',
-  setEntryCopyId: (entryCopyId: string | null, mode: 'copy' | 'cut' = 'copy') =>
-    set({ entryCopyId, entryCopyMode: mode }),
+  setEntryCopyId: (entryCopyId: string | null, entryCopyRundownId: string | null, mode: 'copy' | 'cut' = 'copy') =>
+    set({ entryCopyId, entryCopyRundownId, entryCopyMode: mode }),
 }));