Add OpenCorporates collector for org targets, gated on an API token

Closes the last coverage gap for org (person remains intentionally
unaddressed — no good free/non-scraping option exists). Unlike the
other 8 sources, OpenCorporates now requires an API token even on its
free tier (confirmed: keyless request gets 401). RunnerRegistry::has()
checks services.opencorporates.token is configured before exposing the
source as runnable, so it degrades to "not yet integrated" in the UI
rather than a broken Run button, until OPENCORPORATES_API_TOKEN is set.

Also fixes a real bug hit while building this: a RunnerRegistry::REQUIRES
class constant mapping source key to a closure crashed on file load
(PHP class constants can't hold closures) — inlined the one check
instead of building an abstraction for a single case.

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

config/services.php

@@ -35,4 +35,12 @@ return [
         ],
     ],
 
+    'opencorporates' => [
+        // Free tier requires registering for an account at
+        // opencorporates.com/api_accounts/new — 50 requests/day, 200/month.
+        // Left blank, the source is hidden from "runnable" (see
+        // RunnerRegistry::has()) rather than shown broken.
+        'token' => env('OPENCORPORATES_API_TOKEN'),
+    ],
+
 ];