feat: Phase 4 - Notes + Graph + Wikilinks

- Wikilink parser: [[Title]], [[Title|Display]], [[entity_type:Title]] patterns
- Notes REST API: CRUD under /api/domains/[domainId]/notes/ with wikilink sync
- Note link service: idempotent wikilink resolution, backlinks, outgoing links
- Notes list page: search, filter (all/pinned/archived), domain selector
- Note editor: TipTap with backlinks panel and outgoing links display
- Graph data API: /api/domains/[domainId]/graph and /api/graph
- Graph view page: D3 force-directed graph with entity type filters, search, zoom
- Keyboard shortcuts: g g → graph, c n → new note
- 18 passing wikilink parser tests
- All API routes follow AGENTS.md contract (activity + pg_notify)

apps/web/app/api/domains/[domainId]/notes/[id]/backlinks/route.ts

@@ -0,0 +1,23 @@
+// AGENT INSTRUCTION: After every write (INSERT/UPDATE/DELETE), you MUST:
+// 1. Insert activity feed entry
+// 2. Call pg.notify('project_e_events', JSON.stringify({ type, action, id, workspace_id }))
+// See AGENTS.md for full rules.
+
+import { NextRequest, NextResponse } from 'next/server';
+import { withAuth, requireWorkspaceAccess, createErrorResponse } from '@/lib/auth';
+import { getBacklinks } from '@/lib/note-link-service';
+
+type RouteContext = { params: Promise<{ domainId: string; id: string }> };
+
+// GET /api/domains/[domainId]/notes/[id]/backlinks — List notes that link to this one
+export const GET = withAuth<RouteContext>(async (request: NextRequest, user, context) => {
+  const { domainId, id } = await context!.params;
+  await requireWorkspaceAccess(domainId);
+
+  const backlinks = await getBacklinks(id);
+
+  return NextResponse.json({
+    items: backlinks,
+    totalItems: backlinks.length,
+  });
+});