Add temporary hit points as a separate damage buffer

Temp HP absorbs damage before current HP, cannot be healed, and
does not stack (higher value wins). Displayed as cyan +N after
current HP with a Shield button in the HP adjustment popover.
Column space is reserved across all rows only when any combatant
has temp HP. Concentration pulse fires on any damage, including
damage fully absorbed by temp HP.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/components/hp-adjust-popover.tsx

@@ -1,4 +1,4 @@
-import { Heart, Sword } from "lucide-react";
+import { Heart, ShieldPlus, Sword } from "lucide-react";
 import {
 	useCallback,
 	useEffect,
@@ -12,10 +12,15 @@ const DIGITS_ONLY_REGEX = /^\d+$/;
 
 interface HpAdjustPopoverProps {
 	readonly onAdjust: (delta: number) => void;
+	readonly onSetTempHp: (value: number) => void;
 	readonly onClose: () => void;
 }
 
-export function HpAdjustPopover({ onAdjust, onClose }: HpAdjustPopoverProps) {
+export function HpAdjustPopover({
+	onAdjust,
+	onSetTempHp,
+	onClose,
+}: HpAdjustPopoverProps) {
 	const [inputValue, setInputValue] = useState("");
 	const [pos, setPos] = useState<{ top: number; left: number } | null>(null);
 	const ref = useRef<HTMLDivElement>(null);
@@ -130,6 +135,21 @@ export function HpAdjustPopover({ onAdjust, onClose }: HpAdjustPopoverProps) {
 				>
 					<Heart size={14} />
 				</button>
+				<button
+					type="button"
+					disabled={!isValid}
+					className="inline-flex h-7 w-7 shrink-0 items-center justify-center rounded-md text-cyan-400 transition-colors hover:bg-cyan-400/10 hover:text-cyan-300 disabled:pointer-events-none disabled:opacity-50"
+					onClick={() => {
+						if (isValid && parsedValue) {
+							onSetTempHp(parsedValue);
+							onClose();
+						}
+					}}
+					title="Set temp HP"
+					aria-label="Set temp HP"
+				>
+					<ShieldPlus size={14} />
+				</button>
 			</div>
 		</div>
 	);