Faster first load; demo date tags stay current

First load:
- Draw the Overview as soon as the data arrives instead of on its next
  2-second timer tick (about 2.5 s to 0.6 s on a typical connection).
- Start on DOMContentLoaded instead of window.onload.
- Load the ~900 KB PDF library only when someone exports a PDF.
- Fetch the startup files side by side, and build the docs search index
  after the dashboard has drawn (unless the visit starts on /docs).
- Show a loading placeholder on the Overview until the data arrives.

Demo: the date-batch tags sit on fixed working-day offsets from today.
The seed records them in Demo-Dates.json and the worker relabels them when
the day changes, so a long-running container never looks stale.

README.md

@@ -169,6 +169,8 @@ Compose*) build pack, set the exposed port to **8080**, and attach a domain. The
 reseeds the simulated fleet on every start and needs no volumes or secrets. Times are shown in
 `TZ` (default `America/Chicago`); set it to your own timezone. The demo worker runs
 6 AM to 9 PM every day (`Demo.BusinessHours` in the config) and sleeps overnight.
+The date tags (such as `10/7`) move along each day, so a container that runs for weeks still
+shows this week's deployments.
 
 ### Demo (local PowerShell 7)