feat(notifications): persistent read cursor + delivery history

notification_cursors table stores one read-cursor per user per tenant;
GET /v1/activity returns unreadCount + readAt, POST /v1/activity/read
persists the cursor. Reminder dispatches now append reminder.sent /
reminder.failed system events so delivery history reaches the feed.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

packages/api-client/src/generated/types.ts

@@ -35,6 +35,26 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/v1/activity/read": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get?: never;
+        put?: never;
+        /**
+         * Mark all activity events as read
+         * @description Persists the caller's read cursor — activity events at or before the returned timestamp count as read for this user on subsequent loads.
+         */
+        post: operations["markActivityRead"];
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/v1/admin/stats": {
         parameters: {
             query?: never;
@@ -1161,6 +1181,13 @@ export interface components {
         };
         ActivityFeedResponse: {
             events: components["schemas"]["ActivityEvent"][];
+            /**
+             * Format: date-time
+             * @description Caller's read cursor; absent until the first mark-read
+             */
+            readAt?: string;
+            /** @description Events newer than the caller's persisted read cursor */
+            unreadCount: number;
         };
         AuthResponse: {
             accessToken: string;
@@ -1832,6 +1859,36 @@ export interface operations {
             };
         };
     };
+    markActivityRead: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Read cursor persisted */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": {
+                        /** Format: date-time */
+                        readAt: string;
+                    };
+                };
+            };
+            /** @description Tenant membership not found */
+            404: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+        };
+    };
     getAdminStats: {
         parameters: {
             query?: never;