Retake the dashboard screenshot against a library worth showing (#1623)

The old one photographed a development database: 58 files totalling
7.3 MB, "template-business" and "new-editor" among the largest, two
clients in the storage table, and eight identical "Logged in" rows as
the recent activity. It showed the layout and none of the point.

This one is a plausible installation — real-sounding client
organisations against their quotas, files with names and sizes somebody
would recognise, a month of uploads and downloads with a working week's
rhythm in it, and activity that says what people did rather than that
they arrived. Every widget is on, in the two-column layout, so the
picture also answers "what does this thing actually track".

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -52,7 +52,7 @@ per-seat pricing. It runs on your server, and the files stay there.
 ## Screenshots
 
 <p align="center">
-  <img src=".github/screenshots/dashboard.png" alt="The dashboard, showing counters for files, clients and groups alongside largest files, recent activity and system information" width="900">
+  <img src=".github/screenshots/dashboard.png" alt="The dashboard: counters for files, clients and groups, a month of uploads and downloads as a line chart, the clients using the most storage against their quotas, recent activity, the largest files, system information and API usage" width="900">
 </p>
 <p align="center"><em>The dashboard — what is in the installation, and what has been happening in it.</em></p>