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/ui/src/AppShell.css

@@ -500,6 +500,16 @@ body {
 .ps-command-item .ps-command-icon { width: 20px; text-align: center; opacity: 0.8; }
 .ps-command-item .ps-command-kbd { margin-left: auto; font-size: 12px; color: var(--ps-text-muted); }
 .ps-command-empty { padding: 24px; text-align: center; color: var(--ps-text-muted); }
+.ps-command-group-title {
+  font-size: 11px; font-weight: 700; text-transform: uppercase;
+  letter-spacing: 0.05em; color: var(--ps-text-muted); opacity: 0.7;
+  padding: 10px 12px 4px;
+}
+.ps-command-item .ps-command-subtitle {
+  font-size: 12px; color: var(--ps-text-muted); opacity: 0.8;
+  margin-top: 2px;
+}
+.ps-command-item.is-active .ps-command-subtitle { color: var(--ps-accent-contrast); opacity: 0.9; }
 
 /* ---- Settings ---- */
 .ps-settings { display: flex; flex-direction: column; gap: 8px; margin-bottom: 20px; }