feat(web): make settings tabs URL-addressable via ?tab=

Add an optional `tab` search param (validated against the known tab set)
to /dashboard/settings and drive the Tabs component from it, so each tab
is shareable/bookmarkable (e.g. /dashboard/settings?tab=referral). Tab
clicks update the URL with replace to avoid history spam; existing links
need no search param since `tab` is optional.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/components/settings/settings-content.tsx

@@ -35,7 +35,13 @@ import {
 import { useEffect, useState } from "react";
 import { ChangelogTab } from "./changelog-tab";
 
-export function SettingsContent() {
+export function SettingsContent({
+  tab,
+  onTabChange,
+}: {
+  tab: string;
+  onTabChange: (next: string) => void;
+}) {
   const { t } = useTranslation();
   const { user, signOut } = useAuth();
 
@@ -161,7 +167,7 @@ export function SettingsContent() {
     <div className="mx-auto max-w-3xl space-y-6">
       <h2 className="text-2xl font-bold">{t("settings.title")}</h2>
 
-      <Tabs defaultValue="profile">
+      <Tabs value={tab} onValueChange={onTabChange}>
         <TabsList className="w-full flex-wrap">
           <TabsTrigger value="profile" className="gap-2">
             <User className="h-4 w-4" />