feat(frontend): chat tabs, flat SVG icons, upload autosave, per-user rights

- Chat rework: Chats (private DMs with user search, online dots, unread
  badges) and Team chats tabs; shared message component with reactions,
  edit, image attachments, message search and typing indicators
- Flat modern inline SVG icon set (no external dependency) replaces
  emoji chrome across nav, headers, buttons, tabs and settings
- Uploaded avatar/background images apply instantly (auto-save) with
  confirmation note; per-user permission matrix in dashboard members
- Login localized, invite header uses icon, comment header cleaned

README.md

@@ -22,6 +22,8 @@ light/dark mode. Self-hostable via Node.js or Docker Compose.
 - **Invites + notifications** 🔔 — Pending invites with accept/decline, bell with unread
   badge (polling + realtime push), notifications for invites and chat messages.
 - **Team chat** 💬 — Realtime workspace channel via Socket.IO.
+- **Private chats** ✉️ — 1:1 DMs with reactions, edit, attachments, search, typing,
+  online presence and unread badges; team chats listed per workspace.
 - **Uploads** 📤 — Avatar/background images uploadable (served from `/uploads`).
 - **Calendar** 🗓️ — Deadlines from tasks appear automatically.
 - **Time tracking** ⏱️ — Top-right timer, entries linkable to books, history list.