feat: add delete customer + fix auth form UX

- Backend: DELETE /api/customers/:id removes customer + extensions + logs
- Frontend: delete button on customer detail with confirmation
- Auth form: only sends espocrm_api_key when credentials are entered

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server.py

@@ -492,6 +492,9 @@ class APIHandler(BaseHTTPRequestHandler):
         if re.match(r'/api/customers/\d+/extensions/\d+$', path):
             m = re.search(r'/api/customers/(\d+)/extensions/(\d+)', path)
             self._remove_extension(int(m.group(1)), int(m.group(2)))
+        elif re.match(r'/api/customers/\d+$', path):
+            cid = int(re.search(r'/api/customers/(\d+)', path).group(1))
+            self._delete_customer(cid)
         else:
             self._respond(404, {'error': 'Not found'})
 
@@ -560,6 +563,12 @@ class APIHandler(BaseHTTPRequestHandler):
             (cid, body['extension_id'], body.get('auto_update', True), body.get('license_status', 'active')), fetch=None)
         self._respond(201, {'status': 'ok'})
 
+    def _delete_customer(self, cid):
+        query("DELETE FROM customer_extensions WHERE customer_id = %s", (cid,), fetch=None)
+        query("DELETE FROM deployment_log WHERE customer_id = %s", (cid,), fetch=None)
+        query("DELETE FROM customers WHERE id = %s", (cid,), fetch=None)
+        self._respond(200, {'status': 'ok'})
+
     def _remove_extension(self, cid, ext_id):
         query("DELETE FROM customer_extensions WHERE customer_id = %s AND extension_id = %s", (cid, ext_id), fetch=None)
         self._respond(200, {'status': 'ok'})