feat(channel): pass conversation type through to agent gateway and persist in route

Propagate conversation type (direct/group/thread) from channel adapters
all the way to the agent prompt. Store conversation_type on bot_channel_routes
so the bot knows whether a message originates from a p2p chat, group, or thread.

Schema changes are folded into the 0001 init migration (destructive update).

internal/conversation/flow/resolver.go

@@ -122,6 +122,7 @@ type gatewayIdentity struct {
 	ChannelIdentityID string `json:"channelIdentityId"`
 	DisplayName       string `json:"displayName"`
 	CurrentPlatform   string `json:"currentPlatform,omitempty"`
+	ConversationType  string `json:"conversationType,omitempty"`
 	SessionToken      string `json:"sessionToken,omitempty"`
 }
 
@@ -270,6 +271,7 @@ func (r *Resolver) resolve(ctx context.Context, req conversation.ChatRequest) (r
 			ChannelIdentityID: strings.TrimSpace(req.SourceChannelIdentityID),
 			DisplayName:       r.resolveDisplayName(ctx, req),
 			CurrentPlatform:   req.CurrentChannel,
+			ConversationType:  strings.TrimSpace(req.ConversationType),
 			SessionToken:      req.ChatToken,
 		},
 		Attachments: []any{},