Remove the non-functional WEB pool size admin control

Setting it only rebound main.py's own module-level WEB_POOL_SIZE -
runtime.py and maintenance.py each imported their own copy at process
start (from config import WEB_POOL_SIZE), so the actual pool-sizing
logic in ensure_web_pool()/cleanup_loop never saw the change and kept
targeting the .env value. The UI control only ever changed what the
admin page displayed back to itself, plus a couple of >0/<=0 branch
checks in main.py - never the real pool. Removed the input, button,
JS handler and the dead endpoint rather than wiring the three-module
sync it would take to make it actually work.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/main.py

@@ -1444,8 +1444,6 @@ def admin_page(request: Request, admin: User = Depends(require_admin), db: Sessi
             "pool_status": pool_status,
             "service_health": service_health,
             "web_totals": web_totals,
-            "web_pool_size": WEB_POOL_SIZE,
-            "web_pool_buffer": WEB_POOL_BUFFER,
             "recent_sessions": recent_sessions,
             "open_stats": open_stats,
             "online_sessions": online_sessions,
@@ -3112,16 +3110,6 @@ def delete_category(category_id: int, request: Request, _: User = Depends(requir
     return {"ok": True}
 
 
-@app.put("/api/admin/web-pool-size")
-def update_web_pool_size(payload: dict, request: Request, _: User = Depends(require_admin)):
-    validate_csrf(request)
-    global WEB_POOL_SIZE
-    value = max(0, int(payload.get("size", WEB_POOL_SIZE)))
-    WEB_POOL_SIZE = value
-    ensure_web_pool()
-    return {"ok": True, "size": WEB_POOL_SIZE, "pool": get_web_pool_status()}
-
-
 @app.post("/api/admin/users")
 def create_user(payload: dict, request: Request, _: User = Depends(require_admin), db: Session = Depends(get_db)):
     """The password is never typed by the admin - it's generated here and