Add new tests for shell bridge and broker to handle structured failures and invalid session handling

- Add tests for shell bridge to validate structured error reporting on spawn failures.

- Add broker tests to ensure proper rejection of malformed browser shell upgrades without leaking sensitive tokens.

- Update `.env.example` with `EDGE_PUBLIC_BROKER_URL` for public access configuration.

services/nginx/app/tests/Integration/EdgeGateway/EdgeGatewayBackendIntegrationTest.php

@@ -169,6 +169,14 @@ it('assembles tasks, logs, statistics, operations, commands, and shell lifecycle
             ->and($commandResult['job']['status'] ?? null)
             ->toBe('COMPLETED');
 
+        $context['manager']->recordBrokerPresence(
+            $gatewayId,
+            'connected',
+            'broker-connection-1',
+            null,
+            ['transport' => 'ws']
+        );
+
         $shellSession = $context['manager']->createShellSession(
             $gatewayId,
             (int)$user['id'],
@@ -179,6 +187,8 @@ it('assembles tasks, logs, statistics, operations, commands, and shell lifecycle
         );
         $shellToken = (string)($shellSession['token'] ?? '');
         expect($shellToken)->not->toBe('');
+        expect($shellSession['diagnostics']['broker_presence']['connection_id'] ?? null)
+            ->toBe('broker-connection-1');
 
         $validatedShell = $context['manager']->validateShellSessionToken($shellToken);
         expect($validatedShell)->toHaveKey('status', 'PENDING');
@@ -189,12 +199,21 @@ it('assembles tasks, logs, statistics, operations, commands, and shell lifecycle
         $closedShell = $context['manager']->closeShellSessionByToken(
             $shellToken,
             "edge-shell-output\n",
-            'agent_exit'
+            'agent_exit',
+            [
+                'message' => 'Integration shell completed.',
+                'code' => 0,
+                'stage' => 'shell_active',
+            ]
         );
         expect($closedShell)
             ->toHaveKey('status', 'COMPLETED')
             ->and($closedShell['transcript'] ?? null)
-            ->toBe("edge-shell-output\n");
+            ->toBe("edge-shell-output\n")
+            ->and($closedShell['metadata']['close_reason'] ?? null)
+            ->toBe('agent_exit')
+            ->and($closedShell['metadata']['close_stage'] ?? null)
+            ->toBe('shell_active');
 
         $context['manager']->appendGatewayLogEntry(
             $gatewayId,
@@ -205,14 +224,6 @@ it('assembles tasks, logs, statistics, operations, commands, and shell lifecycle
             ['source' => 'integration']
         );
 
-        $context['manager']->recordBrokerPresence(
-            $gatewayId,
-            'connected',
-            'broker-connection-1',
-            null,
-            ['transport' => 'ws']
-        );
-
         $context['manager']->recordTelemetryFromBroker($gatewayId, [
             'status' => 'ONLINE',
             'metadata' => [