Fix malformed race clock format and refresh docs screenshots

formatRaceClock rendered a doubled-up, garbled time (e.g.
"02:48.20:207") everywhere a race clock is shown - Timing, Overlay,
Results archive, Judging, Training stint logs - because it
concatenated both a centiseconds and a milliseconds computation into
the same string. Only the milliseconds part was ever meant to be
there. Found while building realistic demo data for new screenshots,
since every prior test/demo session was empty and never exercised
this code path with a real result.

Also regenerates all screenshots in docs/screenshots against a
realistic seeded race (drivers, cars, qualifying heats, finals,
practice history, a real judging correction) instead of empty demo
data, adds two new ones (Managed AMMC config, the in-app Guide page)
aimed at helping a new user understand initial setup, removes 6
screenshots orphaned by an earlier README revision, and updates both
README.md and README.sv.md's screenshot tables accordingly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app.js

@@ -5225,13 +5225,10 @@ function formatRaceClock(ms) {
   const s = Math.floor((total % 60000) / 1000)
     .toString()
     .padStart(2, "0");
-  const centiseconds = Math.floor((total % 1000) / 10)
-    .toString()
-    .padStart(2, "0");
   const millis = Math.floor(total % 1000)
     .toString()
     .padStart(3, "0");
-  return `${m}:${s}.${centiseconds}:${millis}`;
+  return `${m}:${s}.${millis}`;
 }
 
 function getSeedMethodLabel(method) {