feat(entity): Chunk #4 remaining items — consistency UI, context rail, palette search, expanded seed & DATA_MODEL

- Consistency tab in EntitiesView surfacing findInconsistencies() results
- ContextRail + MentionPopover wired into WritingView for entity context/hover
- CommandPalette indexes entities and chapters for cross-entity search
- link field type for entity references in character fields
- findDeadCharacterMentions consistency check + tests
- Expand seed with a location, note, and a natural Elias Vell mention so the
  dead-character-after-death case is actually exercised
- Author docs/DATA_MODEL.md documenting core schemas, types, storage contract
- Rename CharacterMention id attr -> entityId to match core backlinks/consistency

packages/editor/src/mention.ts

@@ -103,7 +103,7 @@ export const MentionAutocomplete = Extension.create({
           const nodeType = schema.nodes[CHARACTER_MENTION];
           if (!nodeType) return false;
 
-          const mention = nodeType.create({ id, label });
+          const mention = nodeType.create({ entityId: id, label });
           const tr = state.tr.deleteRange(atPos, from).insert(atPos, mention);
           editor.view.dispatch(tr);
           return true;