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

internal/message/mentions.go

@@ -76,10 +76,13 @@ func (m *MentionHandler) ParseAndNotify(ctx context.Context, channelID, authorID
 	}
 
 	if isEveryone {
-		// Send to all server members
+		// Send to all server members except those who muted this channel
 		rows, err := m.db.QueryContext(ctx,
-			`SELECT user_id FROM members WHERE server_id = $1 AND user_id != $2`,
-			serverID, authorID,
+			`SELECT m.user_id FROM members m
+			 LEFT JOIN notification_settings ns ON ns.user_id = m.user_id AND ns.channel_id = $3
+			 WHERE m.server_id = $1 AND m.user_id != $2
+			   AND (ns.level IS NULL OR ns.level != 'none')`,
+			serverID, authorID, channelID,
 		)
 		if err != nil {
 			m.logger.Error("failed to query server members for @everyone", "error", err)
@@ -141,6 +144,16 @@ func (m *MentionHandler) ParseAndNotify(ctx context.Context, channelID, authorID
 			continue
 		}
 
+		// Check if user muted this channel
+		var level string
+		err = m.db.QueryRowContext(ctx,
+			`SELECT level FROM notification_settings WHERE user_id = $1 AND channel_id = $2`,
+			userID, channelID,
+		).Scan(&level)
+		if err == nil && level == "none" {
+			continue
+		}
+
 		go m.push.SendPush(ctx, userID, payload)
 	}
 }