feat: implement Story 2.2 — ELK.js auto-layout engine in Web Worker

Add automatic diagram layout via ELK.js running in a dedicated Web Worker.
Nodes animate smoothly (200ms ease-out) to computed positions using the
Sugiyama/layered algorithm. Includes layout direction controls (DOWN/RIGHT/
LEFT/UP), edge routing modes (orthogonal/splines/polyline), 200-node soft
cap warning, single-flight race condition protection, and 10s worker timeout.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/package.json

@@ -43,6 +43,7 @@
     "@xyflow/react": "12.10.1",
     "accept-language": "3.0.20",
     "dayjs": "1.11.19",
+    "elkjs": "0.11.0",
     "envin": "catalog:",
     "marked": "16.4.1",
     "motion": "12.23.24",
@@ -73,6 +74,7 @@
     "@turbostarter/eslint-config": "workspace:*",
     "@turbostarter/prettier-config": "workspace:*",
     "@turbostarter/tsconfig": "workspace:*",
+    "@turbostarter/vitest-config": "workspace:*",
     "@types/node": "catalog:node22",
     "@types/react": "catalog:react19",
     "@types/react-dom": "catalog:react19",
@@ -80,7 +82,6 @@
     "eslint": "catalog:",
     "prettier": "catalog:",
     "typescript": "catalog:",
-    "@turbostarter/vitest-config": "workspace:*",
     "vitest": "catalog:"
   }
 }