feat(04-01): add sql.js dependency and graph schema

- Add sql.js ^1.12.0 dependency for WASM SQLite
- Add GRAPH_SCHEMA constant with nodes/edges tables
- Nodes use virtual id from JSON body for upserts
- Edges indexed by source and target for relationship queries

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -32,5 +32,8 @@
   },
   "engines": {
     "node": ">=16.7.0"
+  },
+  "dependencies": {
+    "sql.js": "^1.12.0"
   }
 }