Session 14: Buy All Upgrades (bulk-buy for upgrades) + empty-slot boost leak fix

- Added Game.buyAllUpgrades(): buys every affordable upgrade at once,
  respecting per-upgrade requirements and looping until nothing remains.
- Added a 'Buy All' button to the Upgrades tab header; UI.updateBuyAllButton()
  shows/hides & enables/disables it live each tick based on affordability.
- Fixed empty-slot branch of switchSlot(): added productionBoostUntil: 0 so a
  temporary golden-bloom boost cannot leak into a fresh slot.
- Added .upgrades-header / .buy-all-btn CSS (gold accent theme).

Verified: headless test buy-all-upgrades-test.mjs 24/24 pass; existing
golden-bloom (22/22) and buy-max (6/6) tests re-run clean, no regressions.

js/game.js

@@ -124,6 +124,14 @@ const Game = {
             UI.hideImportModal();
         });
 
+        // Buy All upgrades button.
+        const buyAllBtn = document.getElementById('buy-all-upgrades');
+        if (buyAllBtn) {
+            buyAllBtn.addEventListener('click', () => {
+                Game.buyAllUpgrades();
+            });
+        }
+
         document.getElementById('reset-btn').addEventListener('click', () => {
             if (confirm('Are you sure you want to reset all progress? This cannot be undone!')) {
                 this.reset();
@@ -419,6 +427,48 @@ const Game = {
         return false;
     },
 
+    /**
+     * Buy every upgrade the player can currently afford at once.
+     * Returns an object describing what happened: { bought: count, ids: [...] }.
+     * Upgrades are one-time purchases, so we loop until nothing affordable remains.
+     */
+    buyAllUpgrades() {
+        const bought = [];
+        // Loop until a pass buys nothing (each purchase may unlock new affordability).
+        let progress = true;
+        while (progress) {
+            progress = false;
+            for (const [id, upgrade] of Object.entries(UPGRADES)) {
+                if (this.state.upgrades.includes(id)) continue;
+                // Respect requirements before attempting purchase.
+                if (upgrade.requirements) {
+                    let met = true;
+                    for (const [reqId, reqCount] of Object.entries(upgrade.requirements)) {
+                        if ((this.state.buildings[reqId] || 0) < reqCount) {
+                            met = false;
+                            break;
+                        }
+                    }
+                    if (!met) continue;
+                }
+                if (this.state.stardust >= upgrade.cost) {
+                    this.state.stardust -= upgrade.cost;
+                    this.state.upgrades.push(id);
+                    bought.push(id);
+                    progress = true; // another purchase may have unlocked more affordability
+                }
+            }
+        }
+
+        if (bought.length > 0) {
+            UI.showNotification(`Bought ${bought.length} upgrade(s)!`, 'success');
+            Audio.playPurchase();
+            UI.update();
+        }
+
+        return { bought: bought.length, ids: bought };
+    },
+
     /**
      * Golden Starbloom - random event system.
      * A rare, time-limited bloom occasionally appears on screen. Clicking it
@@ -758,6 +808,9 @@ const Game = {
                 totalPrestigeEssence: this.state.totalPrestigeEssence || 0,
                 prestigeUpgrades: this.state.prestigeUpgrades || [],
                 goldenBlooms: { active: false, timer: 0, lastSpawn: Date.now(), totalClaimed: 0 },
+                // Reset the temporary golden-bloom production boost so a boost
+                // from a previous slot cannot leak into a fresh slot.
+                productionBoostUntil: 0,
                 activeSlot: slot,
                 autoSave: this.state.autoSave
             };