feat(docs): stop hiding half the component API — typed emits, exposes, flow guide

The per-part regex only saw defineEmits<{ inline literal }>(), so a named
interface — how Flow, Popover, Dialog, Menu and Drawer all declare their
events — extracted as zero emits, and defineExpose was not extracted at
all: 36 components' template-ref surfaces were invisible. Consumers
rebuilt what existed (nodeDragStop from @nodes-change, a renderless
child to reach fitView).

- extractor: one type-checking project per components package with a
  virtual <file>.vue.ts mirror per SFC, so cross-file emits interfaces
  (extends included) and expose spreads resolve through the checker —
  ...api expands into the composable's full return with its JSDoc
- parts gain exposes; emits/exposes members carry their JSDoc text;
  update:* model emits get a stock description
- UI: Description column on emits, an Exposes (template ref) table; MCP
  get_doc renders the same
- FlowRoot: JSDoc on every emit and exposed member
- new primitives guide page: building flow graphs — sizing, custom
  nodes, .nodrag, click family, instance API, edge labels

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/app/components/DocsComponentAnatomy.vue

@@ -89,7 +89,12 @@ const roleColor: Record<string, string> = {
             <DocsEmitsTable :emits="part.emits" />
           </div>
 
-          <p v-if="part.props.length === 0 && part.emits.length === 0" class="text-sm text-fg-subtle italic">
+          <div v-if="part.exposes?.length" class="mb-3">
+            <div class="text-[11px] font-semibold uppercase tracking-wider text-fg-subtle mb-2">Exposes (template ref)</div>
+            <DocsExposesTable :exposes="part.exposes" />
+          </div>
+
+          <p v-if="part.props.length === 0 && part.emits.length === 0 && !part.exposes?.length" class="text-sm text-fg-subtle italic">
             No props or events — renders its element and forwards attributes.
           </p>
         </div>