fix(channels): collect contacts for DM and group-mentioned messages (#271)

* fix(channels): collect contacts for DM and group-mentioned messages

Previously, EnsureContact was only called inside the "not mentioned →
record history → return" branch, so contacts were never saved for
messages that the bot actually processed (DMs and group @mentions).
This caused the contacts list to show empty names ("—") for active
users across all channels.

Move contact collection to the main processing path (before
PublishInbound / HandleMessage) so every processed message upserts
the sender's display name. The existing ContactCollector 30-minute
cache prevents redundant DB writes.

Affected channels: Feishu, Telegram, Discord, Slack, Zalo, WhatsApp.

* fix(slack): use clean userID for EnsureContact cache key

The senderID param in HandleMessage is the compound "U123|DisplayName"
form, which produces a different cache key than the clean "U123" used
in the group-history path (handlers.go:178). Use userID (extracted
clean ID) to ensure cache dedup works correctly.

---------

Co-authored-by: Luvu182 <208665161+Luvu182@users.noreply.github.com>
Co-authored-by: viettranx <viettranx@gmail.com>

internal/channels/feishu/bot.go

@@ -131,6 +131,11 @@ func (c *Channel) handleMessageEvent(ctx context.Context, event *MessageEvent) {
 		peerKind = "group"
 	}
 
+	// Collect contact for processed messages (DM + group-mentioned).
+	if cc := c.ContactCollector(); cc != nil {
+		cc.EnsureContact(ctx, c.Type(), c.Name(), mc.SenderID, mc.SenderID, senderName, "", peerKind)
+	}
+
 	metadata := map[string]string{
 		"message_id":    messageID,
 		"chat_type":     mc.ChatType,