feat: add NFT usernames and bot verification (#22)

Implements collectible usernames, official verification workflows, and third-party bot verification after maintainer protocol and migration review.

The composite activity/moderation rating remains an admin-only read model; Telegram Stars Rating wire fields stay unset pending a dedicated official-semantics implementation.

Reviewed-Head: 2796345775ea0f908fb7734601e5e1dee4b653b9
Original-Head: fa082b892fd5180c9c9bc53c81c21cf5d250a75b

Co-authored-by: Egor Egorov <business.egor.sg@gmail.com>

internal/rpc/username_notify.go

@@ -0,0 +1,64 @@
+package rpc
+
+import (
+	"context"
+	"fmt"
+
+	"telesrv/internal/domain"
+)
+
+// NotifyPeerUsernamesChanged is the domain-only edge hook invoked after a
+// collectible username registry mutation commits. It invalidates the cached
+// peer projection and pushes the ordinary non-PTS updateUser/updateChannel
+// refresh to online viewers. The shared projection paths preload the registry
+// once, so fan-out cannot turn the change into an N+1 query.
+func (r *Router) NotifyPeerUsernamesChanged(ctx context.Context, peer domain.Peer) error {
+	if r == nil {
+		return nil
+	}
+	if peer.ID <= 0 {
+		return fmt.Errorf("notify peer usernames changed: invalid peer id %d", peer.ID)
+	}
+	switch peer.Type {
+	case domain.PeerTypeUser:
+		return r.notifyUserUsernamesChanged(ctx, peer.ID)
+	case domain.PeerTypeChannel:
+		return r.notifyChannelUsernamesChanged(ctx, peer.ID)
+	default:
+		return fmt.Errorf("notify peer usernames changed: unsupported peer type %q for peer %d", peer.Type, peer.ID)
+	}
+}
+
+func (r *Router) notifyUserUsernamesChanged(ctx context.Context, userID int64) error {
+	r.invalidateRPCProjectionForUser(userID)
+	if r.deps.Users == nil {
+		return nil
+	}
+	user, found, err := r.verificationUser(ctx, userID)
+	if err != nil {
+		return fmt.Errorf("notify peer usernames changed: load user %d: %w", userID, err)
+	}
+	if !found || user.ID == 0 {
+		return fmt.Errorf("notify peer usernames changed: user %d not found", userID)
+	}
+	return r.NotifyUserModerationFlagsChanged(ctx, user)
+}
+
+func (r *Router) notifyChannelUsernamesChanged(ctx context.Context, channelID int64) error {
+	r.invalidateRPCProjectionForChannel(channelID)
+	if r.deps.Channels == nil {
+		return nil
+	}
+	directory, ok := r.deps.Channels.(verificationChannelDirectory)
+	if !ok {
+		return fmt.Errorf("notify peer usernames changed: channel service does not expose GetChannelByID")
+	}
+	channel, err := directory.GetChannelByID(ctx, channelID)
+	if err != nil {
+		return fmt.Errorf("notify peer usernames changed: load channel %d: %w", channelID, err)
+	}
+	if channel.ID == 0 {
+		return fmt.Errorf("notify peer usernames changed: channel %d not found", channelID)
+	}
+	return r.NotifyChannelChanged(ctx, channel)
+}