feat(phase7): per-channel notification settings and read receipts

Phase 7.1 — Per-channel notification settings
- New notification_settings table (user_id, channel_id, level)
- GET/PUT/DELETE handlers under /channels/{channelID}/notifications
- Push dispatch and @mention loops filtered by notification level
- Frontend: bell icon per channel cycling all/mentions/none

Phase 7.4 — Read receipts
- New read_states table (user_id, channel_id, last_read_message_id)
- PUT /channels/{channelID}/read and GET /users/me/read-states
- Auto-mark-read when messages load in ChatArea
- Unread dot for channels never opened

Also: favicon/icon refresh in index.html

web/src/components/ChatArea.tsx

@@ -6,6 +6,7 @@ import { useMemberStore } from "../stores/member.ts";
 import { useThreadStore } from "../stores/thread.ts";
 import { GiphyPicker, type Gif } from "./GiphyPicker";
 import { MentionDropdown } from "./MentionDropdown";
+import { useReadStatesStore } from "../stores/readStates.ts";
 import { MessageSearch } from "./MessageSearch";
 import { ThreadListPanel } from "./ThreadListPanel.tsx";
 import { ThreadPanel } from "./ThreadPanel.tsx";
@@ -140,6 +141,7 @@ export function ChatArea() {
   const activeChannel = channels.find((c) => c.id === activeChannelId);
   const members = activeServerId ? membersByServer[activeServerId] || [] : [];
   const memberUsernames = useMemo(() => new Set(members.map((m) => m.username)), [members]);
+  const markRead = useReadStatesStore((s) => s.markRead);
 
   useEffect(() => {
     if (activeChannelId) {
@@ -148,6 +150,14 @@ export function ChatArea() {
     }
   }, [activeChannelId, fetchMessages]);
 
+  useEffect(() => {
+    if (!activeChannelId || messages.length === 0 || isLoading) return;
+    const lastMsg = messages[messages.length - 1];
+    if (lastMsg?.id) {
+      markRead(activeChannelId, lastMsg.id);
+    }
+  }, [activeChannelId, messages.length, isLoading]);
+
   useEffect(() => {
     bottomRef.current?.scrollIntoView({ behavior: "auto" });
   }, [messages]);