Start achievement cycling before icon prefetch and request smaller Xbox icon assets

[Copilot]

Achievement rotation was blocked until all Xbox icons finished prefetching, which delayed name/description updates. This change decouples cycle readiness from icon availability and reduces icon payload size by requesting fixed-dimension assets.

• Session readiness and cycle start

  • Xbox session is now marked ready once achievements are fetched/sorted, not after full icon prefetch.
  • Achievement name/description sources can cycle immediately while icon prefetch continues asynchronously.
  • Session-ready contract/comments were updated across Xbox session/monitoring interfaces to reflect the new behavior.

• Icon rendering behavior while downloads are pending

  • On achievement change with a new icon URL, the current icon is cleared immediately (no stale carryover).
  • Text sources continue updating as usual; icon appears only after download + reload completes.
  • If only unlock state changes (same URL), state is updated without redundant image download.

• Xbox icon payload reduction

  • Achievement icon URLs are normalized to request w=200&h=200 image variants.
  • Existing size params are preserved when already present.
  • Media asset URLs are normalized consistently with primary icon URLs.

• Prefetch pacing

  • Reduced per-icon throttle delay in background prefetch to speed cache warmup without making prefetch a gating path.

/* Session is considered ready as soon as achievements are fetched/sorted.
 * Icon prefetching continues in the background and should not block the cycle. */
if (on_ready) {
    on_ready();
}
prefetch_achievement_icons(session->achievements);