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/dist/assets/Settings-y28ROmym.css

@@ -0,0 +1 @@
+.active[data-v-2dca72e5]{border-color:var(--accent);color:var(--accent);font-weight:600}.ok[data-v-2dca72e5]{color:var(--green);font-size:13px;margin-top:10px}.error[data-v-2dca72e5]{margin-top:10px}