feat(ui): add profile client store with LocalStorage persistence

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

src/lib/client/profile.svelte.ts

@@ -0,0 +1,62 @@
+import type { Profile } from '$lib/types';
+
+const STORAGE_KEY = 'kochwas.activeProfileId';
+
+function loadActiveId(): number | null {
+  if (typeof localStorage === 'undefined') return null;
+  const raw = localStorage.getItem(STORAGE_KEY);
+  if (!raw) return null;
+  const n = Number(raw);
+  return Number.isInteger(n) && n > 0 ? n : null;
+}
+
+function saveActiveId(id: number | null): void {
+  if (typeof localStorage === 'undefined') return;
+  if (id === null) localStorage.removeItem(STORAGE_KEY);
+  else localStorage.setItem(STORAGE_KEY, String(id));
+}
+
+class ProfileStore {
+  profiles = $state<Profile[]>([]);
+  activeId = $state<number | null>(null);
+  loaded = $state(false);
+
+  active = $derived(this.profiles.find((p) => p.id === this.activeId) ?? null);
+
+  async load(): Promise<void> {
+    const res = await fetch('/api/profiles');
+    this.profiles = await res.json();
+    const stored = loadActiveId();
+    if (stored && this.profiles.some((p) => p.id === stored)) {
+      this.activeId = stored;
+    }
+    this.loaded = true;
+  }
+
+  select(id: number): void {
+    this.activeId = id;
+    saveActiveId(id);
+  }
+
+  clear(): void {
+    this.activeId = null;
+    saveActiveId(null);
+  }
+
+  async create(name: string, avatar_emoji: string | null): Promise<Profile> {
+    const res = await fetch('/api/profiles', {
+      method: 'POST',
+      headers: { 'content-type': 'application/json' },
+      body: JSON.stringify({ name, avatar_emoji })
+    });
+    if (!res.ok) {
+      const err = await res.json().catch(() => ({ message: 'unknown error' }));
+      throw new Error(err.message ?? 'failed to create profile');
+    }
+    const p = (await res.json()) as Profile;
+    this.profiles = [...this.profiles, p].sort((a, b) => a.name.localeCompare(b.name));
+    return p;
+  }
+}
+
+export const profileStore = new ProfileStore();