Split API docs into per-resource sections under docs/api/ (#2793)

* Split docs/API.md into per-resource sections under docs/api/

* Move API endpoints index above authentication in docs/api/README.md

* Fix trailing comma in boards.md JSON example

* Fix trailing comma in cards.md, add Response label to identity.md, add Rich Text to endpoint index

docs/api/sections/notifications.md

@@ -0,0 +1,62 @@
+# Notifications
+
+Notifications inform users about events that happened in the account, such as comments, assignments, and card updates.
+
+## `GET /:account_slug/notifications`
+
+Returns a list of notifications for the current user. Unread notifications are returned first, followed by read notifications.
+
+__Response:__
+
+```json
+[
+  {
+    "id": "03f5va03bpuvkcjemcxl73ho2",
+    "read": false,
+    "read_at": null,
+    "created_at": "2025-11-19T04:03:58.000Z",
+    "title": "Plain text mentions",
+    "body": "Assigned to self",
+    "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"
+    },
+    "card": {
+      "id": "03f5v9zo9qlcwwpyc0ascnikz",
+      "title": "Plain text mentions",
+      "status": "published",
+      "url": "http://fizzy.localhost:3006/897362094/cards/3"
+    },
+    "url": "http://fizzy.localhost:3006/897362094/notifications/03f5va03bpuvkcjemcxl73ho2"
+  }
+]
+```
+
+## `POST /:account_slug/notifications/:notification_id/reading`
+
+Marks a notification as read.
+
+__Response:__
+
+Returns `204 No Content` on success.
+
+## `DELETE /:account_slug/notifications/:notification_id/reading`
+
+Marks a notification as unread.
+
+__Response:__
+
+Returns `204 No Content` on success.
+
+## `POST /:account_slug/notifications/bulk_reading`
+
+Marks all unread notifications as read.
+
+__Response:__
+
+Returns `204 No Content` on success.