Mirror lane picker into the Account page

Add a "Lanes" section under Account that reuses LanePicker inline, completing
the round trip with Boundaries. Refactor LanePicker to support an `inline`
variant (bare panel vs modal) and apply changes immediately on toggle — so the
account panel needs no explicit save and the home modal now previews the nav
rail live as you pick. Selection still persists through the shared prefs store.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/routes/account/+page.svelte

@@ -9,6 +9,7 @@
   import { openFeedback } from '$lib/feedback.svelte.js';
   import AccountPanel from '$lib/components/AccountPanel.svelte';
   import BoundariesPanel from '$lib/components/BoundariesPanel.svelte';
+  import LanePicker from '$lib/components/LanePicker.svelte';
   import ArticleCard from '$lib/components/ArticleCard.svelte';
 
   let section = $derived($page.url.searchParams.get('section') || 'profile');
@@ -16,11 +17,13 @@
 
   let savedItems = $state([]);
   let savedReady = $state(false);
+  let lanePool = $state(null);
 
   const SECTIONS = [
     { key: 'profile', label: 'Profile' },
     { key: 'saved', label: 'Saved' },
     { key: 'history', label: 'History' },
+    { key: 'lanes', label: 'Lanes' },
     { key: 'boundaries', label: 'Boundaries' },
   ];
 
@@ -29,8 +32,17 @@
     initPrefs();
     initHistory();
     if (auth.user) loadServerHistory();
+    try { lanePool = await getJSON('/api/lanes'); } catch { lanePool = null; }
   });
 
+  let pinnedLaneKeys = $derived(
+    prefs.data.lanes?.length ? prefs.data.lanes : (lanePool?.default ?? [])
+  );
+  function saveLanes(keys) {
+    prefs.data.lanes = keys;
+    persistPrefs();
+  }
+
   // Load the saved grid when entering that section while signed in.
   $effect(() => {
     if (section === 'saved' && auth.user && !savedReady) {
@@ -64,7 +76,14 @@
   </nav>
 
   <div class="content">
-    {#if section === 'boundaries'}
+    {#if section === 'lanes'}
+      {#if lanePool}
+        <LanePicker inline pool={lanePool} selected={pinnedLaneKeys} onsave={saveLanes} />
+      {:else}
+        <p class="muted">Loading…</p>
+      {/if}
+
+    {:else if section === 'boundaries'}
       <BoundariesPanel prefs={prefs.data} onchange={persistPrefs} />
 
     {:else if section === 'history'}