Add modal URL router (#modal=name&tab=key) (#3924)

## Description

Adds a modal URL router so modals can be opened, deep-linked, and
bookmarked via the hash. URLs of the form `#modal=<name>&tab=<key>&...`
open the named modal and pass remaining keys as args to `onOpen`. The
reverse direction also syncs: opening a modal via the UI updates the
URL, closing it clears the hash, and switching tabs updates `&tab=`.

Builds on the BaseModal refactor from #3923.

### What's new

**`ModalRouter.ts`** — small registry + two-way sync helper.
- `register(name, { tag, pageId? })` declares a modal as router-managed
- `routeFromHash()` parses `#modal=...` and dispatches to
`modal.open(args)`
- `syncOpened/syncClosed/syncTab` push state back into the URL via
`history.replaceState` (no history entries)
- A `routingFromUrl` flag prevents URL→modal→URL feedback loops
- Unknown modal names silently strip the hash

**`BaseModal`** — opt-in URL sync via a `routerName` property.
- When set, BaseModal calls into
`modalRouter.syncOpened/syncClosed/syncTab` from `open` / `close` /
`setActiveTab`
- Modals that own their own URL state (lobby modals) just leave
`routerName` undefined

**`Main.ts`** — registers all routable modals and wires the router.
- `handleUrl()`: adds a `modalRouter.routeFromHash()` branch after the
path-based lobby join
- `onHashUpdate`: when the hash is router-managed, routes via the router
instead of tearing down lobby state

### Routable modals

13 inline modals: store, settings, leaderboard, clan, account, help,
news, language, single-player, ranked, troubleshooting,
territory-patterns, flag-input.

Excluded by design: join-lobby, host-lobby (own URL state via
`/game/<id>`), matchmaking (no URL state).

### Example uses

- Deep link to store flags tab: `/#modal=store&tab=flags`
- Settings keybinds tab: `/#modal=settings&tab=keybinds`
- Cosmetics.ts now redirects to `#modal=store&tab=packs` when a
hard-currency purchase fails for insufficient plutonium (after the
alert), so users can top up directly

### URL behavior

- `replaceState` everywhere — no history entries added when modals open
/ close / switch tabs
- Browser back/forward still works for the existing path-based game flow
- `hashchange` events are router-aware so external hash changes (back
button, manual edit) correctly switch between routed modals without
tearing down lobby state

## Please complete the following:

- [x] I have added screenshots for all UI updates _(no visual changes;
smoke-tested in dev)_
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file _(no new user-visible strings)_
- [ ] I have added relevant tests to the test directory _(no test
coverage; manually tested URL load, UI open, tab switch, close,
hashchange, insufficient-plutonium redirect)_
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

DISCORD_USERNAME

src/client/components/BaseModal.ts

@@ -1,5 +1,6 @@
 import { html, LitElement, TemplateResult } from "lit";
 import { property, query, state } from "lit/decorators.js";
+import { modalRouter } from "../ModalRouter";
 import "./baseComponents/Modal";
 import type { OModalTab } from "./baseComponents/Modal";
 
@@ -57,6 +58,13 @@ export abstract class BaseModal extends LitElement {
     return {};
   }
 
+  /**
+   * Optional router name. When set, BaseModal syncs URL state on open/close/
+   * tab change as `#modal=<routerName>&tab=<key>&...`. Modals that own their
+   * own URL state (e.g. lobby modals) should leave this undefined.
+   */
+  protected routerName?: string;
+
   /** Render slot="header" content. Default: no header slot. */
   protected renderHeaderSlot(): TemplateResult | null {
     return null;
@@ -149,19 +157,24 @@ export abstract class BaseModal extends LitElement {
       if (tabs.length && this.activeTab === "") {
         this.activeTab = tabs[0].key;
       }
-      if (
-        typeof args?.tab === "string" &&
-        tabs.some((t) => t.key === args.tab)
-      ) {
-        this.activeTab = args.tab;
-      }
+      const requestedTab =
+        typeof args?.tab === "string" && tabs.some((t) => t.key === args.tab)
+          ? args.tab
+          : null;
 
       const wasOpen = this.isModalOpen;
       if (!wasOpen) {
+        if (requestedTab) this.activeTab = requestedTab;
         this.registerEscapeHandler();
+        this.onOpen(args);
+        if (this.activeTab) this.onTabEnter(this.activeTab);
+      } else {
+        this.onOpen(args);
+        // Already open: route tab changes through setActiveTab so URL syncs.
+        if (requestedTab && requestedTab !== this.activeTab) {
+          this.setActiveTab(requestedTab);
+        }
       }
-      this.onOpen(args);
-      if (this.activeTab) this.onTabEnter(this.activeTab);
 
       if (wasOpen) return;
 
@@ -176,6 +189,10 @@ export abstract class BaseModal extends LitElement {
       } else {
         this.modalEl?.open();
       }
+
+      if (this.routerName) {
+        modalRouter.syncOpened(this.routerName, args);
+      }
     } finally {
       this.opening = false;
     }
@@ -193,6 +210,10 @@ export abstract class BaseModal extends LitElement {
     } else {
       this.modalEl?.close();
     }
+
+    if (this.routerName) {
+      modalRouter.syncClosed(this.routerName);
+    }
   }
 
   // ---- Tab management ----
@@ -204,6 +225,9 @@ export abstract class BaseModal extends LitElement {
     if (this.activeTab === key) return;
     this.activeTab = key;
     this.onTabEnter(key);
+    if (this.routerName) {
+      modalRouter.syncTab(this.routerName, key);
+    }
   }
 
   // ---- Internals ----

src/client/components/RankedModal.ts

@@ -9,6 +9,8 @@ import { modalHeader } from "./ui/ModalHeader";
 
 @customElement("ranked-modal")
 export class RankedModal extends BaseModal {
+  protected routerName = "ranked";
+
   @state() private elo: number | string = "...";
   @state() private userMeResponse: UserMeResponse | false = false;
   @state() private errorMessage: string | null = null;