Step 6.3 Follow-up: Implement §31.4 full URL resolution

- Implemented §31.4 same-origin resolution during discovery
- Validated genericity scan correctly via full recursive check
- Generated browser screenshots for 5.2/5.3 verification

src/connection.js

@@ -38,7 +38,7 @@ export class ExhibitConnection {
   async attach() {
     if (!this.frame || this.loading) return;
     const generation = this.generation;
-    try { await this.host.connect(this.transport(this.frame)); }
+    try { await this.host.connect(this.transport(this.frame), this.url); }
     catch (error) { if (generation === this.generation && !error.code) this.host.report(error); }
     this.changed();
   }