`GET /templates` — list all built-in templates in registry order. Authenticated (any valid session) but **scope-free**: the static built-in catalog carries no tenant data, so it takes `AuthContext` to require a login and performs no grant/scope check.

[  {    "columns": [      {        "data_type": "string",        "description": "string",        "extraction": "string",        "name": "string",        "nullable": true      }    ],    "description": "string",    "id": "string",    "label": "string",    "mechanisms": [      {        "default": true,        "http": null,        "input_format": "string",        "mechanism": "string"      }    ],    "ocsf": {      "activity_id": 0,      "category_uid": 0,      "class_uid": 0,      "type_uid": 0    },    "requires_ingestion_features": [      "string"    ],    "status": "verified",    "suggestions": {      "table_description": "string",      "table_name": "string"    },    "version": 0  }]