wip: save-on-pause + mobile touch fix

- Auto-save on visibilitychange (tab switch), window blur, and beforeunload
- touch-action: manipulation on all buttons to prevent double-tap zoom on mobile
- From EPIC #57 task 6: mobile polish items

index.html

@@ -67,6 +67,7 @@ body{background:var(--bg);color:var(--text);font-family:'SF Mono','Cascadia Code
 .build-btn.can-buy{border-color:#2a3a4a;background:#0e1420}
 .build-btn.can-buy:hover{border-color:var(--accent);box-shadow:0 0 8px var(--glow)}
 .build-btn:disabled{opacity:0.3;cursor:not-allowed}
+.build-btn,.project-btn,.ops-btn,.main-btn{touch-action:manipulation}
 .b-name{color:var(--accent);font-weight:600}.b-count{float:right;color:var(--gold)}.b-cost{color:var(--dim);display:block}.b-effect{color:var(--green);display:block;font-size:9px}
 .project-btn{display:block;width:100%;text-align:left;padding:6px 10px;margin-bottom:4px;border-radius:4px;cursor:pointer;font-family:inherit;font-size:10px;background:#0c0c18;border:1px solid var(--border);color:var(--text);transition:all 0.15s}
 .project-btn.can-buy{border-color:#3a2a0a;background:#141008}