Add Holehe collector for email targets

Closes the email target-type gap (previously had zero collectors).
Checks whether an email is registered on 120+ sites via the
password-reset-oracle technique. Shares the Sherlock/whois venv.

HoleheRunner gates success on the CSV file existing rather than the
process exit code: holehe's CLI calls Python's exit("message") right
after writing results on its normal success path, which always yields
exit code 1 regardless of outcome — discovered while verifying this
end-to-end against the real dev server and queue worker.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

database/seeders/SourceSeeder.php

@@ -49,6 +49,13 @@ class SourceSeeder extends Seeder
                 'target_types' => ['ip'],
                 'runner' => 'http:ip-api',
             ],
+            [
+                'key' => 'holehe',
+                'name' => 'Holehe',
+                'description' => 'Checks whether an email address is registered on 120+ sites via the password-reset-oracle technique.',
+                'target_types' => ['email'],
+                'runner' => 'python:holehe',
+            ],
         ];
 
         foreach ($sources as $source) {