Add freshness bar, enhance overlays and renderers

- Add enemy freshness tracking (novelty bonus for repeated deploys)
- Add freshness bar to sidepanel enemy cards with penalty indicator
- Major overhaul of renderer-overlays.js (790+ lines for UI polish)
- Enhanced combat log, shop overlays, and inventory UI
- Improved weapon/upgrade display with partial ownership colors
- Added element icons and weakness/resistance indicators to cards
- Enhanced radial menu and tooltip system
- Add "stale/%" penalty text when freshness depleted
- Update play link to ffazeshift.net in index.html

js/utils.js

@@ -39,7 +39,11 @@ function clamp(value, min, max) {
 }
 
 function cheapestEnemyCost() {
-  return ENEMY_DEFS.reduce((min, d) => Math.min(min, d.cost), Infinity);
+  const tier = G?.difficultyTier ?? 0;
+  const prestige = G?.prestigeLevel ?? 0;
+  return ENEMY_DEFS
+    .filter(d => (d.minTier ?? 0) <= tier && (d.minPrestige ?? 0) <= prestige)
+    .reduce((min, d) => Math.min(min, d.cost), Infinity);
 }
 
 function countAliveEnemies() {