chore: remove dead code orphaned by topbar redesign (#4)

The new topbar's "Refresh all" button replaces the old SSE-driven
"Load All" link and progress UI. With those gone, several pieces of
infrastructure had no callers left:

- GET /api/load-all-players, POST /api/populate-database, and
  GET /api/database-status — SSE endpoints with no frontend consumers
- #progress-section / #loading divs in players + courses pages
- .progress-container / .progress-bar / .progress-text / .loading CSS
- public/js/progress.js script (defines fetchRatingsWithProgress, never
  called, and loadAllPlayers, no longer wired) — to be deleted manually
  since the sandbox blocks rm

public/css/shared.css

@@ -306,15 +306,6 @@ body {
     margin: 0 0 24px 0;
 }
 
-/* ── Loading ──────────────────────────────────── */
-
-.loading {
-    text-align: center;
-    padding: 40px 20px;
-    font-size: 15px;
-    color: var(--text-secondary);
-}
-
 /* ── Tables ───────────────────────────────────── */
 
 table {