feat(entity): Chunk #4 data layer + entity UI (characters & world-building)

Data layer:
- Fuzzy scorer (packages/core/src/fuzzy.ts) with index recovery + unit tests
- Backlink computation (packages/core/src/backlinks.ts) incl. entity-level backlinks
- Consistency checker (packages/core/src/consistency.ts) incl. reciprocity/scope + unit tests
- StorageAdapter contract extended with listEntities/searchEntities/saveEntity/deleteEntity;
  implemented in Local (Dexie) and Server adapters; contract tests cover entity CRUD + ?q= search
- WorldItem.fields now supports list values (keyPeople, rivals); expanded RelationshipKind
- @mention autocomplete extension + picker in the editor package

Entity UI (apps/web/src/features/entities/):
- Generic field renderer (EntityFields) driven by ENTITY_FIELDS/FieldDef
- Tabbed directory with fuzzy search + entity cards (EntitiesView)
- Create/edit/delete drawer (EntityEditor) reusing shared fields
- Relationship editor + force-directed SVG relationship map
- Entity engine stylesheet; wired into nav

Store: project-store entity methods (load/create/update/delete) over the StorageAdapter contract.

CI-green: typecheck, lint, 65 tests, and web build all pass.

packages/ui/src/AppShell.css

@@ -126,6 +126,115 @@ body {
   line-height: var(--ps-font-leading, 1.75);
 }
 
+/* ---- Writing surface: toolbar, focus/typewriter modes ---- */
+.ps-writing {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+.ps-writing-toolbar {
+  display: flex;
+  align-items: center;
+  gap: 16px;
+  padding: 8px 16px;
+  border-bottom: 1px solid var(--ps-border);
+  background: var(--ps-surface);
+  flex: none;
+}
+.ps-chapter-select {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+.ps-chapter-select-label {
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.06em;
+  color: var(--ps-text-muted);
+}
+.ps-chapter-select select {
+  padding: 6px 10px;
+  border: 1px solid var(--ps-border);
+  border-radius: 8px;
+  background: var(--ps-canvas);
+  color: var(--ps-text);
+  font-size: 13px;
+  font-family: inherit;
+}
+.ps-toolbar-group {
+  display: flex;
+  gap: 4px;
+}
+.ps-tool {
+  padding: 5px 12px;
+  border: 1px solid transparent;
+  border-radius: 8px;
+  background: transparent;
+  color: var(--ps-text-muted);
+  font-size: 13px;
+  font-family: inherit;
+  cursor: pointer;
+}
+.ps-tool:hover {
+  color: var(--ps-text);
+  background: var(--ps-canvas);
+}
+.ps-tool.is-active {
+  color: var(--ps-text);
+  border-color: var(--ps-accent);
+  background: color-mix(in srgb, var(--ps-accent) 12%, transparent);
+}
+.ps-autosave-indicator {
+  margin-left: auto;
+  display: flex;
+  align-items: center;
+  gap: 7px;
+  font-size: 12px;
+  color: var(--ps-text-muted);
+}
+.ps-autosave-dot {
+  width: 7px;
+  height: 7px;
+  border-radius: 50%;
+  background: var(--ps-text-muted);
+}
+.ps-autosave-indicator[data-status="saving"] .ps-autosave-dot {
+  background: #d9a441;
+}
+.ps-autosave-indicator[data-status="dirty"] .ps-autosave-dot {
+  background: #d96c4b;
+}
+.ps-autosave-indicator[data-status="saved"] .ps-autosave-dot {
+  background: #4f9d69;
+}
+
+/* Focus mode: dim the whole document, then restore the block under the cursor. */
+.ps-editor-focus .ps-editor-content {
+  opacity: 0.22;
+  transition: opacity 0.15s ease;
+}
+.ps-editor-focus .ps-editor-content .ps-focus-active,
+.ps-editor-focus .ps-editor-content .ps-focus-active * {
+  opacity: 1;
+  transition: opacity 0.05s ease;
+}
+
+.ps-writing-status {
+  display: flex;
+  gap: 16px;
+  align-items: center;
+  padding: 6px 16px;
+  border-top: 1px solid var(--ps-border);
+  background: var(--ps-surface);
+  color: var(--ps-text-muted);
+  font-size: 12px;
+  flex: none;
+}
+.ps-writing-status-note {
+  margin-left: auto;
+  color: var(--ps-text);
+}
+
 /* ---- Sidebar nav ---- */
 .ps-logo {
   font-weight: 700;