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

apps/web/src/features/entities/EntityFields.tsx

@@ -12,6 +12,14 @@ import { ENTITY_FIELDS } from "@pubscript/core";
 import { Input } from "@pubscript/ui";
 import { Select } from "@pubscript/ui";
 
+/** A short display label for an entity, regardless of kind. */
+export function entityLabel(e: Entity): string {
+  if ("body" in e) {
+    return e.body.trim().slice(0, 40) || "(untitled note)";
+  }
+  return e.name;
+}
+
 /** Read a field value from an entity, regardless of where it is stored. */
 export function getFieldValue(e: Entity, key: string): string | string[] {
   if ("fields" in e) {
@@ -40,12 +48,15 @@ export function fieldsFor(e: Entity): FieldDef[] {
 interface EntityFieldsProps {
   entity: Entity;
   onChange: (patch: Partial<Entity>) => void;
+  /** All entities in the book, used to resolve `link` field references. */
+  entities?: Entity[];
 }
 
 function renderField(
   field: FieldDef,
   value: string | string[],
   onChange: (v: string | string[]) => void,
+  entities?: Entity[],
 ) {
   const label = (
     <label className="ps-field-label">
@@ -79,9 +90,22 @@ function renderField(
       );
     case "list":
       return <TagField value={Array.isArray(value) ? value : []} onChange={onChange} />;
-    case "link":
+    case "link": {
+      const opts = (entities ?? [])
+        .filter((e) => e.id !== value)
+        .map((e) => ({ value: e.id, label: entityLabel(e) }));
+      return (
+        <div>
+          {label}
+          <Select
+            value={typeof value === "string" ? value : ""}
+            options={[{ value: "", label: "— none —" }, ...opts]}
+            onChange={(ev) => onChange(ev.target.value)}
+          />
+        </div>
+      );
+    }
     case "text":
-    default:
       return (
         <div className="ps-field-span-2">
           {label}
@@ -146,7 +170,7 @@ function TagField({
   );
 }
 
-export function EntityFields({ entity, onChange }: EntityFieldsProps) {
+export function EntityFields({ entity, onChange, entities }: EntityFieldsProps) {
   const fields = fieldsFor(entity);
 
   return (
@@ -157,6 +181,7 @@ export function EntityFields({ entity, onChange }: EntityFieldsProps) {
             field,
             getFieldValue(entity, field.key),
             (v) => onChange({ [field.key]: v } as Partial<Entity>),
+            entities,
           )}
         </div>
       ))}