Subscription upgrade/downgrade + tier management (#3927)

## Summary

- Tier upgrade/downgrade in the Store. The Subscriptions tab now shows
all tiers including the user's current one. Other tiers swap "Subscribe"
→ "Switch" when the user already has a sub, and clicking them calls the
new `POST /subscriptions/@me/change-tier` endpoint with a
direction-aware confirm (upgrade charges prorated diff now, downgrade
gives account credit).
- Owned-tier card renders a **Current Plan** badge in place of the
purchase button. Resolution logic in `resolveCosmetics` now reads
`userMeResponse.player.subscription.tier` (with flare fallback) and
marks that tier as `owned`.
- AccountModal's `<subscription-panel>` reworked into a proper
two-column layout:
- **Left**: tier name, `$X.XX/mo` price, description, daily Pu/Caps
amounts.
- **Right**: status badge (Active / Renews date / Cancels date),
`[Manage] [Change Tier]` button row, `[Cancel]` centered underneath.
When `cancelAtPeriodEnd === true`, the row collapses to a single
`[Reactivate]` button (opens the Stripe portal).
- New `<o-button size="xs">` variant (`py-2 px-3 text-xs`) for the
compact panel buttons.
- Store dollar-purchase price label now supports an optional suffix
(`/mo` for subs only) via a `priceSuffix` prop plumbed through
`CosmeticContainer` → `PurchaseButton`.
- `Api.ts` gains `changeSubscriptionTier(tierName)` with the same
401-handling pattern as the existing subscription helpers.


<img width="1114" height="728" alt="Screenshot 2026-05-14 at 7 09 20 PM"
src="https://github.com/user-attachments/assets/688f83d5-4010-4580-9214-6885af8ec98e"
/>

<img width="1038" height="276" alt="Screenshot 2026-05-14 at 7 09 33 PM"
src="https://github.com/user-attachments/assets/458197f5-a0d4-4c32-bc55-31e5679629b5"
/>

<img width="887" height="286" alt="Screenshot 2026-05-14 at 7 09 55 PM"
src="https://github.com/user-attachments/assets/8149ed82-89cc-4bbe-83de-3614f886b331"
/>

## Discord

evan

src/client/components/baseComponents/Button.ts

@@ -3,7 +3,7 @@ import { customElement, property } from "lit/decorators.js";
 import { translateText } from "../../Utils";
 
 type ButtonVariant = "primary" | "secondary" | "danger" | "ghost";
-type ButtonSize = "sm" | "md" | "lg";
+type ButtonSize = "xs" | "sm" | "md" | "lg";
 type ButtonWidth = "auto" | "block" | "blockDesktop" | "fill";
 type IconPosition = "left" | "right" | "only";
 
@@ -45,6 +45,8 @@ export class OButton extends LitElement {
   private sizeClasses(): string {
     if (this.iconPosition === "only") {
       switch (this.size) {
+        case "xs":
+          return "w-6 h-6 text-xs";
         case "sm":
           return "w-8 h-8 text-sm";
         case "md":
@@ -54,6 +56,8 @@ export class OButton extends LitElement {
       }
     }
     switch (this.size) {
+      case "xs":
+        return "py-1 px-2 text-xs";
       case "sm":
         return "py-1.5 px-3 text-sm";
       case "md":