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/DocsEmitsTable.vue

@@ -12,6 +12,7 @@ defineProps<{
         <tr class="bg-bg-subtle text-left">
           <th class="py-2.5 px-4 font-medium text-fg-muted text-xs uppercase tracking-wider">Event</th>
           <th class="py-2.5 px-4 font-medium text-fg-muted text-xs uppercase tracking-wider">Payload</th>
+          <th class="py-2.5 px-4 font-medium text-fg-muted text-xs uppercase tracking-wider">Description</th>
         </tr>
       </thead>
       <tbody>
@@ -22,6 +23,10 @@ defineProps<{
           <td class="py-2.5 px-4">
             <code class="text-xs font-mono text-fg-muted bg-bg-inset px-1.5 py-0.5 rounded border border-border wrap-break-word">{{ e.payload }}</code>
           </td>
+          <td class="py-2.5 px-4 text-fg-muted min-w-48">
+            <DocsText v-if="e.description" :text="e.description" />
+            <span v-else>—</span>
+          </td>
         </tr>
       </tbody>
     </table>