Keep working out the home page cards after startup (closes #211)

Server.Start ran the loop that works out the home page's cards on the
context it was given. fx ends that context once start-up is done, so the
cards were worked out once and never again. The loop now runs on a
context that only Stop ends, as the other background parts do. Stop
waits for the loop to return, until its own context ends, before it
stops the HTTP server.

A new test starts a server in a synctest bubble and ends its context at
once. On the bubble's fake clock, the cards must be worked out again a
minute later, and not after Stop.

Model: opus-5-5

TODO.md

@@ -35,6 +35,9 @@ tested.
 
 # Completed Steps
 
+- 2026-10-27: the server works out the home page's cards every minute until it
+  stops. It used to work them out only once, at startup: the end of the context
+  that `Start` is given stopped the refreshes (closes #211)
 - 2026-10-27: README "Rationale" says why RouteWatch exists: to answer our other
   services' questions about IP addresses, from its own routing table and the
   WHOIS details it keeps. It still says what RIS Live does not give (closes