feat(ui): 3-tab UI per spec — admin dashboard + date filter, personal dashboard, training w/ difficulty, settings profile

Tab 1 Admin overview (/): aggregate stats + DATE FILTER (?from&to), hardest personas,
admin quick actions (Users / + Add product).
Tab 2 My dashboard (/my/board): per-user win/lose/session summary (works for admin too).
Tab 3 Training (/training): product list w/ status + persona count; admins see all groups
(draft->analyze/edit), trainees see ready->personas; persona list shows DIFFICULTY (1-5
stars); admins get a Manage-personas button.
Settings (/settings): profile (name/email) via new PATCH /api/auth/profile + change
password + language.
Backend: analytics date filter; profile endpoint; /api/me/board + /api/chat/sessions
opened to any authed user.
Rebuilt frontend/dist.

frontend/src/api/index.js

@@ -36,6 +36,7 @@ export const api = {
   login: (username, password) => request('POST', '/api/auth/login', { username, password }),
   me: () => request('GET', '/api/auth/me'),
   setup: (b) => request('POST', '/api/auth/setup', b),
+  updateProfile: (b) => request('PATCH', '/api/auth/profile', b),
   adminCreateUser: (b) => request('POST', '/api/admin/users', b),
   adminListUsers: () => request('GET', '/api/admin/users'),
   adminUpdateUser: (username, b) => request('PUT', `/api/admin/users/${username}`, b),
@@ -54,5 +55,11 @@ export const api = {
   weakAreas: () => request('GET', '/api/me/weak-areas'),
   myPersonas: () => request('GET', '/api/me/personas'),
   generatePersona: (b) => request('POST', '/api/me/personas/generate', b),
-  analytics: () => request('GET', '/api/analytics'),
+  analytics: (params = {}) => {
+    const qs = new URLSearchParams()
+    if (params.from) qs.set('from', params.from)
+    if (params.to) qs.set('to', params.to)
+    const q = qs.toString()
+    return request('GET', `/api/analytics${q ? `?${q}` : ''}`)
+  },
 }