Add a new Pins section to docs/API.md covering pin/unpin and the pinned cards list response.

Author: svara

docs/API.md

@@ -803,6 +803,79 @@ __Response:__
 
 Returns `204 No Content` on success.
 
+## Pins
+
+Pins let users keep quick access to important cards.
+
+### `POST /:account_slug/cards/:card_number/pin`
+
+Pins a card for the current user.
+
+__Response:__
+
+Returns `204 No Content` on success.
+
+### `DELETE /:account_slug/cards/:card_number/pin`
+
+Unpins a card for the current user.
+
+__Response:__
+
+Returns `204 No Content` on success.
+
+### `GET /my/pins`
+
+Returns the current user's pinned cards. This endpoint is not paginated and returns up to 100 cards.
+
+__Response:__
+
+```json
+[
+  {
+    "id": "03f5vaeq985jlvwv3arl4srq2",
+    "number": 1,
+    "title": "First!",
+    "status": "published",
+    "description": "Hello, World!",
+    "description_html": "<div class=\"action-text-content\"><p>Hello, World!</p></div>",
+    "image_url": null,
+    "tags": ["programming"],
+    "golden": false,
+    "last_active_at": "2025-12-05T19:38:48.553Z",
+    "created_at": "2025-12-05T19:38:48.540Z",
+    "url": "http://fizzy.localhost:3006/897362094/cards/4",
+    "board": {
+      "id": "03f5v9zkft4hj9qq0lsn9ohcm",
+      "name": "Fizzy",
+      "all_access": true,
+      "created_at": "2025-12-05T19:36:35.534Z",
+      "url": "http://fizzy.localhost:3006/897362094/boards/03f5v9zkft4hj9qq0lsn9ohcm",
+      "creator": {
+        "id": "03f5v9zjw7pz8717a4no1h8a7",
+        "name": "David Heinemeier Hansson",
+        "role": "owner",
+        "active": true,
+        "email_address": "david@example.com",
+        "created_at": "2025-12-05T19:36:35.401Z",
+        "url": "http://fizzy.localhost:3006/897362094/users/03f5v9zjw7pz8717a4no1h8a7",
+        "avatar_url": "http://fizzy.localhost:3006/897362094/users/03f5v9zjw7pz8717a4no1h8a7/avatar"
+      }
+    },
+    "creator": {
+      "id": "03f5v9zjw7pz8717a4no1h8a7",
+      "name": "David Heinemeier Hansson",
+      "role": "owner",
+      "active": true,
+      "email_address": "david@example.com",
+      "created_at": "2025-12-05T19:36:35.401Z",
+      "url": "http://fizzy.localhost:3006/897362094/users/03f5v9zjw7pz8717a4no1h8a7",
+      "avatar_url": "http://fizzy.localhost:3006/897362094/users/03f5v9zjw7pz8717a4no1h8a7/avatar"
+    },
+    "comments_url": "http://fizzy.localhost:3006/897362094/cards/4/comments"
+  }
+]
+```
+
 ## Comments
 
 Comments are attached to cards and support rich text.