Feature: Add Spall Liner toggle to Tankopedia model viewer

## Summary
- Add a Spall Liner toggle button to the Tankopedia model viewer, placed alongside the existing Calibrated Shells / Enhanced Armor buttons. It's only shown for tanks that can actually equip Spall Liner.
- The toggle reads/writes the same `Duel.protagonist.provisions` array as the Provisions tab, so both stay in sync automatically.
- If a provision slot is free, clicking equips Spall Liner immediately. If all slots are full, a popover shows icons with a shuffle arrow so you can pick which active provision to swap out in one step.
- Buttons use the same medium rounding as the consumable buttons on the tank page.
- When Spall Liner is equipped, the Dynamic Armor 3D viewer's click-damage tooltip now applies the same 20% HE damage reduction Spall Liner grants in-game.
- Refactored the hardcoded `-0.2` HE damage coefficient in `tankCharacteristics.ts` into a shared constant so the Compare tool and the 3D viewer use a single source of truth.

## Scope
This only affects the single-tank Tankopedia page. The Firepower stats table (the viewed tank's own outgoing gun damage) is intentionally untouched, since a defensive damage reduction would be semantically backwards there. The Dynamic Armor viewer's click tooltip is the only place a "damage taken by this tank" number exists, so that's where the reduction is wired in.

packages/website/src/core/blitzkit/spallLiner.ts

@@ -0,0 +1,8 @@
+export const SPALL_LINER_PROVISION_ID = 101;
+
+/**
+ * Matches the in-game reduction Spall Liner grants against HE splash
+ * damage. Shared between the characteristics panel and the Dynamic
+ * Armor 3D viewer's damage readout so the figure isn't duplicated.
+ */
+export const SPALL_LINER_HE_DAMAGE_DELTA = -0.2;

packages/website/src/core/blitzkit/tankCharacteristics.ts

@@ -22,6 +22,7 @@ import {
 } from "@blitzkit/core";
 import { coefficient } from "@blitzkit/core/src/blitzkit/coefficient";
 import type { EquipmentMatrix } from "../../stores/duel";
+import { SPALL_LINER_HE_DAMAGE_DELTA } from "./spallLiner";
 import { defaultEqualizer } from "./tankToDuelMember";
 
 export type TankCharacteristics = ReturnType<typeof tankCharacteristics>;
@@ -170,7 +171,10 @@ export function tankCharacteristics(
     coefficient(
       [applyReactiveArmor && shell.type !== ShellType.SHELL_TYPE_HE, -0.27],
       [applyDynamicArmor, -0.1],
-      [applySpallLiner && shell.type === ShellType.SHELL_TYPE_HE, -0.2],
+      [
+        applySpallLiner && shell.type === ShellType.SHELL_TYPE_HE,
+        SPALL_LINER_HE_DAMAGE_DELTA,
+      ],
     );
   const assaultDamageCoefficient =
     gun.assault_ranges && gun.assault_ranges.types.includes(shell.type)